Bluetooth: tester: Support BR L2CAP listen mode

If cp->transport is BTP_L2CAP_TRANSPORT_BREDR, register BR L2CAP
server.

If cp->transport is not one of BTP_L2CAP_TRANSPORT_BREDR and
BTP_L2CAP_TRANSPORT_LE, return error code BTP_STATUS_FAILED.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>