call: protect rtpStreams with callMutex

+ add callMutex_ around rtpStreams_ access to avoid use after free.
+ retrigger setRotation, because it's called from pjsip and we
need to avoid any potential wrong lock order.
+ Fix ut_conference by protecting pInfos_ checks

Change-Id: Ie423c06b1d1f2ef6532afd3144d0667b8f709498