Fix API breakage on Header.Unmarshal

[Sean-Der]

Return (int, error) and not just error

[Sean-Der]

@stv0g @aler9 This was the plan I believe? After this lands I can start tagging v1 off of master branch again.

[codecov]

Codecov Report

Patch coverage: 83.33% and project coverage change: -0.04 ⚠️

Comparison is base (5d59489) 87.53% compared to head (9478ee9) 87.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #228      +/-   ##
==========================================
- Coverage   87.53%   87.50%   -0.04%     
==========================================
  Files          20       20              
  Lines        1877     1880       +3     
==========================================
+ Hits         1643     1645       +2     
- Misses        204      205       +1     
  Partials       30       30              

Flag	Coverage Δ
go	87.50% <83.33%> (-0.04%)	⬇️
wasm	86.54% <83.33%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packet.go	88.21% <83.33%> (-0.19%)	⬇️

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[aler9]

@Sean-Der the change that you want to restore was part of the backward-incompatible PR #119, that was included in v1.7.0 and that i intentionally left out in my previous PR. Prior to v1.7.0, signature of Header.Unmarshal was

rtp/packet.go

Line 81 in 4997f55

func (h *Header) Unmarshal(rawPacket []byte) error { //nolint:gocognit

after v1.7.0, signature is

rtp/packet.go

Line 78 in ccb8b11

func (h *Header) Unmarshal(buf []byte) (n int, err error) { //nolint:gocognit

Therefore, this PR restores compatibility with v1.7.x but breaks compatibility with v1.6.5. Probably it's better to merge it since version v1.7.x has surely more users than v1.6.x.

[Sean-Der]

@aler9 thanks for the explanation. What a mess :(

I will get some tooling setup to make sure this doesn’t happen again.