macvlan: Move skb_clone check closer to call

Currently macvlan calls skb_clone in macvlan_broadcast but checks
for a NULL return in macvlan_broadcast_one instead.  This is
needlessly confusing and may lead to bugs introduced later.

This patch moves the error check to where the skb_clone call is.

The only other caller of macvlan_broadcast_one never passes in a
NULL value so it doesn't need the check either.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Thanks,
Reviewed-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>