Broadcaster: Don't pass a nil context into grpc call or it panics

[thomshutt]

What does this pull request do? Explain your changes. (required)
Stops a panic in the case we detect an existing session after creating one

Specific updates (required)

• Pass context.Background() instead of nil into the gRPC call

How did you test each of these updates (required)

• Ran unit tests

Does this pull request close any open issues?
Fixes #2585

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[codecov]

Codecov Report

Merging #2586 (47f5e9c) into master (6bf2087) will increase coverage by 0.00269%.
The diff coverage is 73.13433%.

@@                 Coverage Diff                 @@
##              master       #2586         +/-   ##
===================================================
+ Coverage   56.42997%   56.43266%   +0.00269%     
===================================================
  Files             88          88                 
  Lines          18857       18888         +31     
===================================================
+ Hits           10641       10659         +18     
- Misses          7637        7650         +13     
  Partials         579         579                 

Impacted Files	Coverage Δ
eth/client.go	5.16039% <0.00000%> (-0.11779%)	⬇️
server/mediaserver.go	67.66744% <96.07843%> (+0.84501%)	⬆️
discovery/discovery.go	89.16667% <0.00000%> (-2.50000%)	⬇️

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Impacted Files	Coverage Δ
eth/client.go	5.16039% <0.00000%> (-0.11779%)	⬇️
server/mediaserver.go	67.66744% <96.07843%> (+0.84501%)	⬆️
discovery/discovery.go	89.16667% <0.00000%> (-2.50000%)	⬇️

[cyberj0g]

It seems that explicitly marking connection as being initialized will allow to remove that rarely invoked and not covered 'rollback' code path. See my changes.

Edit: looks like there were a number of race conditions in registerConnection and elsewhere, we indirectly encountered only one of them. Hope it's better with this fix.

[cyberj0g]

Thanks for review @yondonfu, all addressed.

[yondonfu]

LGTM. The refactored connection handling code seems cleaner and easier to reason about 👍 .

Before merging please update CHANGELOG_PENDING to reflect that this PR resolves the linked issue in a different way than the original PR title/description.