Unset device trust state before unpairing.

a) Device is trusted.
b) Device is unpaired.
c) We need to set the trusted value before unpairing.

Else on the next pairing, the device will be trusted automatically
and we will not show the PBAP authentication dialog.

Change-Id: I8d7c962688885885d37be341e5494069294eb392
1 file changed