Support GCM ciphers even if ENABLE_EXTERNAL_AUTH is defined.

With ENABLE_EXTERNAL_AUTH, external auth will only be used depending
on the selected cipher (allowed for non-GCM, not allowed for GCM).

BUG=webrtc:5222, chromium:628400

Review-Url: https://codereview.webrtc.org/2720663003
Cr-Original-Commit-Position: refs/heads/master@{#16955}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d48f488bed37e8a5af47bd4be85d9b819fa284b4
6 files changed