Always startOrMigrate connection when caps change

This is a simplification whose main point is to make
regular the recovery mechanisms. When a new NC is found,
there is now a central function that can always be called
no matter the state, which is valuable because it can be
copied in other cases where a change is necessary. The
prime example of this will be changes of LP.

Bug: 269715746
Test: VpnTest
Change-Id: I7981668ea091db5103b749eb80502e9ba348d4f3