bridge: Split may_deliver/deliver_clone out of br_flood

This patch moves the main loop body in br_flood into the function
may_deliver.  The code that clones an skb and delivers it is moved
into the deliver_clone function.

This allows this to be reused by the future multicast forward
function.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>