Handle out of sequence disconnect event in DcTracker.

Ignore disconnect event if ApnContext is in CONNECTING state.
When entering DcRetrying state, if phone is in OOS, first notify
Dc retrying event and then disconnected event.
This ensures ApnContext will always move out of CONNECTING
state before disconnecting.

Change-Id: I1c83326be18bec7f41327d9a8d4c1839c0016354
CRs-Fixed: 828349