base-call: treat 'ringing-in' as an in-call state

So that we setup in-call events as soon as we get the incoming call
ringing in. This allows us to have plugin-specific implementations
e.g. reporting call termination when the remote caller hangs up.

src/mm-base-call.c

@@ -673,6 +673,7 @@ mm_base_call_get_path (MMBaseCall *self)
 /* Define the states in which we want to handle in-call events */
 #define MM_CALL_STATE_IS_IN_CALL(state)         \
     (state == MM_CALL_STATE_DIALING ||          \
+     state == MM_CALL_STATE_RINGING_IN  ||      \
      state == MM_CALL_STATE_RINGING_OUT ||      \
      state == MM_CALL_STATE_ACTIVE)