[NETLABEL]: Shrink the genl-ops registration code.

Turning them to array and registration in a loop saves
80 lines of code and ~300 bytes from text section.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>