drivers/net: Omit check for multicast bit in netdev_for_each_mc_addr

There is no need to check for the address being a multicast address in
the netdev_for_each_mc_addr loop, so remove it. This patch covers all
remaining network drivers still containing such a check.

Cc: Joe Perches <joe@perches.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>