Add pkg/media/h264reader

H264Reader reads a stream of Annex B H264 and packetizes into a NAL at a
time. This then can easily be passed into pion/rtp

Add RTPTransceiver.SetSender

This non-standard API allows us to re-use existing transceivers.
The WebRTC API causes SDP bloat right now since it doesn't allow
the re-use of existing media sections.

hold lock for checkNegotiationNeeded transceiver checks

Fix sender nil on negotiation check step 5.3.1

Update pion/ice

v2.0.8 => v2.0.9

Don't lose packet for OnTrack PayloadType probe

Dropping a packet at the beginning of every track is bad, since
it corrupts the first keyframe of each video track.  This works
by adding a peek method to Track, and using it in NewTrack.

The peeked data is protected by the RWLock already associated
with the track.  We check for its presence with the reader lock
taken, which avoids taking the writer lock (or doing an atomic read)
in the common case (no peeked data).

Fixes pion#1001

Update CI configs to v0.4.7

Update lint scripts and CI configs.

Fix conversion from untyped int

New issue with Go v1.15, already fixed in master

Update module pion/sdp/v3 to v3.0.1

Generated by renovateBot

Update pion/sctp and pion/datachannel vers

Relates to pion#1396