[webrtc-pc] new commits pushed by aboba

The following commits were just pushed by aboba to https://github.com/w3c/webrtc-pc:

* Fix Respec link error
  by Jan-Ivar Bruaroey
https://github.com/w3c/webrtc-pc/commit/21a2ead2ff26dc6336883cf5831dca0bbd949e0e

* Merge pull request #1878 from jan-ivar/descriptionslots2

Fix Respec link error
  by Bernard Aboba
https://github.com/w3c/webrtc-pc/commit/49237a946c465cee8651badb110c15b7553e9dde