tests: Bluetooth: BR: Add test suite RFCOMM_server

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

Add shell commands to create and manage RFCOMM server with different
flow control mechanisms.

In the test suite, there are seven test cases:
Case 1: RFCOMM Server - Reject RFCOMM Session. IUT should properly
reject incoming RFCOMM session when BR connection is disconnected.
Case 2: RFCOMM Server - Forward compatible with Bluetooth devices that
do not send PN command. IUT should properly handle this case and use
FCON/FCOFF as flow control.
RPN, Test) and send NSC responses
Case 3: RFCOMM Server - Respond to Control Commands After DLC
Establishment. IUT should properly respond to control commands (RLS,
RPN, Test) and send NSC responses.
Case 4: RFCOMM Server - Information Transfer with Aggregate Flow
Control. IUT should handle information transfer with aggregate flow
control and properly issue flow control signals.
Case 5: RFCOMM Server - Information Transfer with Credit Based Flow
Control and Active Disconnection. IUT should handle credit-based flow
control and actively disconnect DLC.
Case 6: RFCOMM Server - Information Transfer with Credit Based Flow
Control and Passive Disconnection. IUT should handle credit-based flow
control and respond to DLC disconnection.

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