[automerger skipped] Add an implementation of SipTransportImplBase for testing am: d2da7b2861 am: 8ad242f9c5 am: 1c73293cd6 am: 3075e93bc6 -s ours

am skip reason: Change-Id I740d1f3c7ea61072fb4b119144cdfbf7f3f181b0 with SHA-1 0f572fcef8 is in history

Original change: https://android-review.googlesource.com/c/platform/packages/services/Telephony/+/1453559

Change-Id: I2fc5fa62d337a7424dcc49131ddfbc8488856caa