Update API for Objective-C RTCIceServer

BUG=

Review URL: https://codereview.webrtc.org/1499653003

Cr-Original-Commit-Position: refs/heads/master@{#11000}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: aa32c3e537643eb71d8a8cb8ea7089f8cda2098a
16 files changed