Parse params needed for SipDelegate routing

Add getViaBranchParameter and getCallId parameter to SipMessage
API in order to allow the SipDelegate to quickly route SipMessages
without requiring the app to peak into the headers.

Bug: 181591815
Test: atest CtsTelephonyTestCases
Change-Id: Iac94f73335ac5caa634b31c10a675aaf91c13af7