Merge third_party/libsrtp from https://chromium.googlesource.com/chromium/deps/libsrtp.git at 98284c8600c73812ff4716a6ea157d1e11d417dc

This commit was generated by merge_from_chromium.py.

Change-Id: I8b474cb15707650e0e2ab4ea5afd07917f18f292