net: Remove unused parameter from fill method in fib_rules_ops.

The netlink message header (struct nlmsghdr) is an unused parameter in
fill method of fib_rules_ops struct.  This patch removes this
parameter from this method and fixes the places where this method is
called.

(include/net/fib_rules.h)

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>