Bluetooth: tester: Support BR L2CAP connect and disconnect BTP command

Change the channel id rage of BR L2CAP channel to
`ARRAY_SIZE(channels)` ~ `ARRAY_SIZE(channels) + CHANNELS`. The
unified channel ID can help identify whether the channel is BR or BLE
L2CAP channel.

When the address type of L2CAP connect command is
`BTP_BR_ADDRESS_TYPE`, create BR L2CAP channel connect request.

And if the channel ID falls into the range `ARRAY_SIZE(channels)`
~ `ARRAY_SIZE(channels) + CHANNELS` of L2CAP disconnect command,
create BR L2CAP disconnect request.

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