[ptp4u] signaling messages done by workers

[leoleovich]

Summary

Currently server directly responds to the signaling messages (grants).
However, we already have powerful mechanism of sending messages (sync/fwup/announce/delayResp) via workers.
This change will leverage workers to send grants, completely removing send logic from the server.
This will unblock cancellation messages being generated within the subscription on cancel.

Test Plan

Tcpdump/Wireshard

Works in prod

Unittests

Lint issue is unrelated

[leoleovich]

Lint issue is unrelated ^

[codecov-commenter]

Codecov Report

Merging #201 (d57cde4) into main (f5cf74e) will decrease coverage by 0.03%.
The diff coverage is 57.47%.

@@            Coverage Diff             @@
##             main     #201      +/-   ##
==========================================
- Coverage   60.89%   60.86%   -0.04%     
==========================================
  Files          86       86              
  Lines        7910     7916       +6     
==========================================
+ Hits         4817     4818       +1     
- Misses       2657     2663       +6     
+ Partials      436      435       -1     

Impacted Files	Coverage Δ
ptp/ptp4u/server/config.go	85.71% <ø> (ø)
ptp/ptp4u/server/server.go	35.06% <40.00%> (-0.36%)	⬇️
ptp/ptp4u/server/worker.go	56.75% <56.41%> (-2.38%)	⬇️
ptp/ptp4u/server/subscription.go	98.52% <100.00%> (+0.01%)	⬆️

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[vvfedorenko]

There are too many copy-paste lines of code for each message type in the worker go-routine. Could we factorise it? Or I can do it in separate PR

[leoleovich]

They are all kinda different. Some send via event socket and read TX timestamp, some send via general and don't. We could make it nicer I suppose. But not sure making this diff even bigger is good :)

[vvfedorenko]

OK, NVM, I will clean it up later