Make Client always commit params

[edaniels]

Description

Without this, there's a race (see test change) where we can send messages with the wrong reliability guarantees after Client returns and before it processes its DCEP ACK message. This can easily happen if a DataChannel is created via a Dial and Accept flow where there's no OnOpen and the starts writing immediately.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 69.70%. Comparing base (02dc2ec) to head (998a790).

Files	Patch %	Lines
datachannel.go	66.66%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #196      +/-   ##
==========================================
+ Coverage   68.83%   69.70%   +0.87%     
==========================================
  Files           4        4              
  Lines         308      307       -1     
==========================================
+ Hits          212      214       +2     
+ Misses         70       68       -2     
+ Partials       26       25       -1     

Flag	Coverage Δ
go	69.70% <66.66%> (+0.87%)	⬆️
wasm	69.70% <66.66%> (+0.87%)	⬆️

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[edaniels]

@Sean-Der merging. This should be harmless and the test properly fails when I undo the fix.