interfaces: fix network-manager plug

[mvo5]

Add networkManagerPermanentPlugSecComp that adds socket AF_NETLINK - KOBJECT_UEVENT to unbreak nmcli.

We should squash-merge this and then cherry-pick it for 2.27.

[stolowski]

LGTM.

[zyga]

Permanent plug? Why not connected?

[zyga]

LGTM

[codecov-io]

Codecov Report

Merging #3818 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #3818      +/-   ##
==========================================
- Coverage   75.86%   75.84%   -0.03%     
==========================================
  Files         403      403              
  Lines       34835    34907      +72     
==========================================
+ Hits        26427    26474      +47     
- Misses       6535     6555      +20     
- Partials     1873     1878       +5

Impacted Files	Coverage Δ
interfaces/builtin/network_manager.go	72.72% <0%> (-5.33%)	⬇️
cmd/snap/cmd_aliases.go	93.33% <0%> (-1.67%)	⬇️
daemon/api.go	72.45% <0%> (-0.18%)	⬇️
cmd/snap/cmd_snap_op.go	63.63% <0%> (-0.11%)	⬇️
overlord/snapstate/snapstate.go	80.7% <0%> (+0.04%)	⬆️
overlord/snapstate/snapmgr.go	79.33% <0%> (+0.07%)	⬆️
client/snap_op.go	79.47% <0%> (+0.27%)	⬆️

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[mvo5]

We will need to squash merge this to make the 2.27 cherry pick simpler.

[jdstrand]

LGTM, +1

[niemeyer]

@jdstrand Sending the +1 and the change requests (or even relevant comments) with the actual review feature of GH makes your review tracked both in the summary at the right above, and also in our review board.