Fix logic error in CarrierService.

CarrierService is supposed to filter intents in onBind and only accept
valid actions. The logic was off so that it rejected all bind attempts.

This was tricky to track down because clients get no clear signal that
onBind is returning null.

Bug: 21571360
Change-Id: Id82fce8dfa73a75fae1ce69f73b922addc7daa3e