Return useful error for incorrect channel type

[Sean-Der]

Before (Wrapped for linter)

invalid Message Type &{%!s(datachannel.ChannelType=0)
%!s(uint16=256) %!s(uint32=0) initial_data_channel }

Now (Wrapped for linter)

expected and actual message type does not match, wanted ACK
got Open ChannelType(PartialReliableRexmitUnordered) Priority(500)
ReliabilityParameter(750) Label(Sean) Protocol(Test)

Resolves #125
Resolves pion/webrtc#2258

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 19 lines in your changes are missing coverage. Please review.

Project coverage is 65.84%. Comparing base (f56395b) to head (f55406a).

❗ Current head f55406a differs from pull request most recent head c45cc49. Consider uploading reports for the commit c45cc49 to get more accurate results

Files	Patch %	Lines
message_channel_open.go	0.00%	16 Missing ⚠️
message_channel_ack.go	0.00%	2 Missing ⚠️
datachannel.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #201      +/-   ##
==========================================
- Coverage   69.70%   65.84%   -3.87%     
==========================================
  Files           4        4              
  Lines         307      325      +18     
==========================================
  Hits          214      214              
- Misses         68       86      +18     
  Partials       25       25              

Flag	Coverage Δ
go	65.84% <0.00%> (-3.87%)	⬇️
wasm	65.84% <0.00%> (-3.87%)	⬇️

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