Fix AVDT_open before Delay_report according to AVDTP v1.3

According to AVDTP v1.3, A first Delay Report shall be sent immediately after the SEP has been configured.
This is before entering the OPEN state from IDLE/CONFIGURED.

Send AVDT_SCB_API_OPEN_REQ_EVT after receiving delay report from SNK.

Tag: #compatibility

Bug: 171432373

Test:  atest BluetoothInstrumentationTests

Change-Id: I87901c901315f0d18f5f7273a20b8e8f6e578449