Add subid to SipTransportImplBase#createSipDelegate

1) Add subId to the createSipDelegate method to make subId transitions
easier.
2) Add sub id torn down destroy reason
3) Small improvements found during implementation

Bug: b/154763999
Test: atest TeleServiceTests
Change-Id: I2d140ddfde65955a0833f610eeeeaf9d02b0f170