[NETFILTER] bridge: code rearrangement for clarity
Cleanup and rearrangement for better style and clarity:
Split the function nf_bridge_maybe_copy_header into two pieces
Move copy portion out of line.
Use Ethernet header size macros.
Use header file to handle CONFIG_NETFILTER_BRIDGE differences
Signed-off-by: Stephen Hemminger <shemminger@osdl.org> Signed-off-by: David S. Miller <davem@davemloft.net>