feat(docker): expose netem-extension packet filters on kernel links

Surface the netem extensions delivered in uBridge feature/tc-netem-ext
as GNS3 filter types: rate (tc-style bandwidth string), reorder (needs
delay), gemodel (Gilbert-Elliot bursty loss, exclusive with
packet_loss), duplicate, seed and limit, plus the delay jitter
distribution and the loss/dup correlation parameters. All are
kernel-datapath only — the relay's packet-filter registry has no
equivalent, so available_filters hides them on relay links, setting one
on a created relay link returns 409, and the project-load path drops
them with a warning (update_filters runs before the datapath is
decided, so it cannot reject there). Validation mirrors the tc grammar:
reorder requires delay, gemodel and packet_loss are mutually exclusive,
a distribution requires jitter > 0, rate is integer+unit capped at
100gbit.

The translation in DockerVM._netem_command_parts emits the frozen
grammar order and gates extension keywords on the 'tc capabilities'
netem token list (probed once per uBridge process; a plain
delay/loss/corrupt/dup filter never probes, keeping old uBridge builds
untouched; the correl suffix has no token and gates on 'rate' as the
extension-build marker).

Reconcile became reset-before-set: the kernel's netem change merges
optional attributes (rate, correlation, reorder, corrupt, gemodel,
distribution, seed keep their previous value when the new message omits
them), so removing a parameter needs an explicit 'tc reset' — the
bpf_drop filters are re-added right after in the same flow, so the
clsact churn is invisible. The capability check runs before the reset
so a failed update leaves the previous qdisc in place.

e2e (isolated instance, kernel link): 24/24 — rate 512kbit adds exactly
2x the per-packet serialization to the RTT (45.5 ms for 1400-byte
pings), paretonormal jitter + rate-cleared leak check, reorder gap 5,
gemodel 50% bursty loss, duplicate, loss 30% correl 50%, seed 42 +
limit 5000 visible in the qdisc dump, suspend/resume and node restart
keep the filters, relay link rejects rate with 409, teardown leaves no
netem. Full unit suite: 1916 passed.

gns3server/schemas/compute/nios.py

@@ -35,7 +35,11 @@ class UDPNIO(BaseModel):
     rhost: str = Field(..., description="Remote host")
     rport: int = Field(..., gt=0, le=65535, description="Remote port")
     suspend: Optional[bool] = Field(None, description="Suspend the NIO")
-    filters: Optional[dict] = Field(None, description="Packet filters")
+    filters: Optional[dict] = Field(
+        None,
+        description="Packet filters (relay-supported types only: delay/packet_loss/corrupt/frequency_drop/bpf — "
+        "the netem extensions need a kernel-datapath NIO)",
+    )
     markers: Optional[dict] = Field(None, description="Traffic-insight markers")
 
 
@@ -74,10 +78,12 @@ class BridgeNIO(BaseModel):
     Kernel-datapath bridge Network Input/Output properties. The NIO tells the
     node to enslave its veth host end into the named kernel bridge instead of
     wiring a uBridge UDP relay. Impairment filters run on the veth host end:
-    delay/packet_loss/corrupt as one tc netem qdisc, bpf as cls_bpf match-drop
-    classifiers (needs a uBridge reporting cbpf). frequency_drop still has no
-    kernel equivalent and is rejected. Markers and packet capture are served
-    by uBridge's AF_PACKET modules on the veth host end.
+    delay/packet_loss/corrupt and the netem extensions (rate, reorder,
+    gemodel, duplicate, seed, limit, jitter distributions, loss correlation)
+    as one tc netem qdisc, bpf as cls_bpf match-drop classifiers (needs a
+    uBridge reporting cbpf). frequency_drop still has no kernel equivalent
+    and is rejected. Markers and packet capture are served by uBridge's
+    AF_PACKET modules on the veth host end.
     """
 
     type: BridgeNIOType
@@ -85,7 +91,8 @@ class BridgeNIO(BaseModel):
     suspend: Optional[bool] = Field(None, description="Suspend the NIO")
     filters: Optional[dict] = Field(
         None,
-        description="Packet filters served on the veth host end (delay/packet_loss/corrupt via netem, bpf via cls_bpf)",
+        description="Packet filters served on the veth host end (delay/packet_loss/corrupt and the netem extensions "
+        "via one tc netem qdisc, bpf via cls_bpf)",
     )
     markers: Optional[dict] = Field(None, description="Traffic-insight markers (attached to the veth host end)")