tests: Bluetooth: BR: Add test suite RFCOMM_client

IUT works as an RFCOMM Client. The peer device, RFCOMM server, is a PC
running bumble.

Add following test cases:

Case 6, RFCOMM MTU Size Data Send/Receive Test. To verify that the RFCOMM
client can correctly send and receive data packets that are exactly equal
to the negotiated MTU size.

Case 7, RFCOMM Data Transfer Exceeding MTU Size Test. To verify that the
RFCOMM client can reject sending and receiving data packets that exceed
the negotiated MTU size.

Case 8, RFCOMM Disconnect and Reconnect Test. To verify that the RFCOMM
client can properly handle a normal RFCOMM disconnection and successfully
reestablish the connection.

Case 9, RFCOMM Recovery After ACL Disconnection Test. To verify that the
RFCOMM client can properly recover when the underlying ACL connection is
abruptly disconnected, by reestablishing both ACL and RFCOMM connections.

Signed-off-by: Jiawei Yang <jiawei.yang_1@nxp.com>