Reset AG state on discarding outgoing connection attempt

Outgoing HFP connection attempt is abandoned if the peer device manages
to connect the HFP first. AG connection instance allocated for the
outgoing connection attempt is reset but the state remains
BTA_AG_OPENING_ST. When this connection instance is allocated again for
the subsequent connection attempts, this leftover state causes the
connection attempts to fail locally.

Test: Manual | Connect/Disconnect with buds over BR/EDR transport
Test: mmm packages/modules/Bluetooth
Flag: com.android.bluetooth.flags.reset_ag_state_on_collision
Bug: 339906876
Bug: 341376713
Change-Id: I8dc6959607dea006ce2df0acae99f0db289fb17a