interfaces/builtin: sync connected slot and permanent slot snippet

[morphis]

The connected plug snippet allows sending any method call from
a connected plug to the service but the corresponding snippet for
the slot denied receiving anything other than PropertiesChanged.

See https://forum.snapcraft.io/t/udisks2-interface-doesnt-allow-to-use-dbus-properties-interface/902
for more details.

[jdstrand]

Approved.

Note that I corrected the description of this PR.

[morphis]

@jdstrand Thanks!

[codecov-io]

Codecov Report

Merging #3470 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3470      +/-   ##
==========================================
- Coverage   77.16%   77.15%   -0.02%     
==========================================
  Files         373      373              
  Lines       25793    25793              
==========================================
- Hits        19904    19900       -4     
- Misses       4132     4135       +3     
- Partials     1757     1758       +1

Impacted Files	Coverage Δ
interfaces/builtin/udisks2.go	82.5% <ø> (ø)	⬆️
interfaces/sorting.go	93.33% <0%> (-3.34%)	⬇️
cmd/snap/cmd_aliases.go	94% <0%> (-2%)	⬇️
overlord/snapstate/snapstate.go	81.28% <0%> (-0.24%)	⬇️
overlord/ifacestate/helpers.go	65.54% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1383502...e4d03d6. Read the comment docs.

[zyga]

+1

[renat-galimov]

Thanks!