TTY: ircomm, revamp locking

Use self->spinlock only for ctrl_skb and tx_skb. TTY stuff is now
protected by tty_port->lock. This is needed for further cleanup (and
conversion to tty_port helpers).

This also closes the race in the end of close.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Samuel Ortiz <samuel@sortiz.org>
Cc: netdev@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>