Calling this API causes a race condition with RtpSession::start().
The former needs the latter to be run first, this was not enforced,
causing a crash by nullptr access on socketPair_ member.
This patch checks for a non-nullptr socketPair_ to procceed the restart.

Issue: #81987
Change-Id: I20886fe70398f018621aade1c7bac3ff15ef9055