l2cap_chan_put() is exported, so export also l2cap_chan_hold() for
modules.
l2cap_chan_hold() has use case in net/bluetooth/6lowpan.c
Signed-off-by: Pauli Virtanen <pav@iki.fi> Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>