batman-adv: Drop per algo GW section class code

This code was  only used in the past for the sysfs interface. But since
this was replace with netlink, it was never executed. The function pointer
was only checked to figure out whether the limit 255 (B.A.T.M.A.N. IV) or
2**32-1 (B.A.T.M.A.N. V) should be used as limit.

So instead of keeping the function pointer, just store the limits directly
in struct batadv_algo_gw_ops.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>