Add tests for SipTransportImplBase

Adds two tests for SipTransportImplBase, the first is to create
and destroy a SipDelegate and ensure that
createSipDelegate/destroySipDelegate is called and the death recipient
is linked/unlinked. The second calls binderDied to ensure that any
existing SipDelegates are correctly cleaned up upon phone process
death.

Bug: 195148134
Test: atest FrameworksTelephonyTests:SipTransportImplBaseTest
Change-Id: I84ec863eac5589e7412666180ad1a314da1b3110