bond: cleanup netpoll code

This started out with fixing a sparse warning, then I realized that
the wrapper function bond_netpoll_info could just be removed
by rolling it into the enable code.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>