net: bridge: drop skb2/skb0 variables and use a local_rcv boolean

Currently if the packet is going to be received locally we set skb0 or
sometimes called skb2 variables to the original skb. This can get
confusing and also we can avoid one conditional on the fast path by
simply using a boolean and passing it around. Thanks to Roopa for the
name suggestion.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>