feat(docker): eBPF stateful packet filters on kernel links

Consume the eBPF impairment classifier delivered in uBridge
feature/tc-precision: frequency_drop becomes the exact every-Nth mode
(tc nth_drop; -1 = drop everything maps to every 1st) and the new
kernel-only quota type is the byte-cap mode (tc quota_drop, 100 = hard
cutoff). KERNEL_UNSUPPORTED_FILTERS is gone entirely — kernel/relay
eligibility is now purely topological. Both modes gate on ebpf=1 from
the per-process tc capabilities probe (error names the setcap fix); the
cleanup path (modes off) only talks to the eBPF commands when the probe
reported them. Reconcile is a plain re-set: the netem reset-before-set
already detaches the program and clears uBridge's per-interface
registry, so a mode set after it is a fresh load+attach.

Documented semantic difference: the relay counts both directions
through one bridge counter, the kernel counts per direction — N=3
round-trip loss is 1-(2/3)^2 = 55.6% on kernel vs ~1/N on relay
(measured 57%). window_drop is NOT exposed: the delivered
implementation advances the window with no gap, making 'outside the
window packets pass' unreachable (needs outage/period fields —
recorded in the spec); flow_drop awaits a parameter-shape decision.

Also fixes a pre-existing restart bug the e2e exposed: _bridges (relay
bridge names) was never cleared on stop, so restarting a node with a
relay link skipped 'bridge create' and failed on add_nio_udp.

e2e (isolated instance): 13/13 — pref-1 tc_impair classifier on both
veths, 57% round-trip for N=3, -1 = exact 100%, quota hard cutoff,
delay coexistence, clean teardown, suspend/resume, node restart,
relay-leg frequency_drop regression through an Ethernet switch. Full
suite: 1925 passed.

gns3server/compute/base_manager.py

@@ -375,17 +375,6 @@ class BaseManager:
             nio.suspend = nio_settings.get("suspend", False)
         elif nio_settings["type"] == "nio_bridge":
             nio = NIOBridge(nio_settings["bridge"])
-            # Impairment filters with a tc netem equivalent run on the veth
-            # host end; the relay-only types are rejected here (the controller
-            # already keeps them off kernel links — this is the second guard).
-            from gns3server.utils.packet_filter_validation import KERNEL_UNSUPPORTED_FILTERS
-
-            unsupported = KERNEL_UNSUPPORTED_FILTERS.intersection(nio_settings.get("filters") or {})
-            if unsupported:
-                raise ComputeError(
-                    "Packet filter(s) {} cannot run on a kernel-datapath link "
-                    "(no uBridge relay in the forwarding path)".format(", ".join(sorted(unsupported)))
-                )
             nio.filters = nio_settings.get("filters", {})
             # Markers ride the NIO and attach to the veth host interface via
             # uBridge's AF_PACKET marker module (marker add_kernel).