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/compute/base_node.py

@@ -1116,6 +1116,17 @@ class BaseNode:
         :param filters: Array of filter dictionary
         """
 
+        # The netem-extension filters (rate, reorder, gemodel…) only exist on
+        # the kernel datapath. The controller keeps them off relay links;
+        # this is the second guard for direct compute API use.
+        from gns3server.utils.packet_filter_validation import kernel_only_features
+
+        kernel_only = kernel_only_features(filters)
+        if kernel_only:
+            raise NodeError(
+                "Packet filter(s) {} only run on a kernel-datapath link (tc netem on the "
+                "veth host end); the uBridge relay has no equivalent".format(", ".join(sorted(kernel_only)))
+            )
         await self._ubridge_send("bridge reset_packet_filters " + bridge_name)
         for packet_filter in self._build_filter_list(filters):
             cmd = f"bridge add_packet_filter {bridge_name} {packet_filter}"