Bluetooth: RFCOMM: Add a argument `server` to `bt_rfcomm_server.accept`

In current implementation, the `accept` cannot be identified if the
same one `accept` callback is passed by the upper layer.

Similar with `accept` of `bt_l2cap_server.accept`, add a parameter
`server` to the `bt_rfcomm_server.accept` callback.

Add a argument `server` to function bt_hfp_hf_accept() to avoid
building issue for HFP_HF.

Add a argument `server` to function rfcomm_accept() to avoid building
issue for shell/rfcomm.c.

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