Add mutex to the supplicant aidl_return_util
to support multiple clients to the service.

Some OEMs have additional clients to the
supplicant service, aside from the Wifi
framework. This can lead to contention
in the HAL.

Bug: 358741598
Test: Manual test - connect to Wifi
Test: atest VtsHalWifiSupplicantStaIfaceTargetTest \
            VtsHalWifiSupplicantStaNetworkTargetTest \
            VtsHalWifiSupplicantP2pIfaceTargetTest
Change-Id: Ice7bb5dec5ebf618ebb603a996b80954710eb78b
1 file changed