Do not modify or load balance ARP packets passing through balance-alb
mode (wherein the ARP did not originate locally, and arrived via a bridge).

Modifying pass-through ARP replies causes an incorrect MAC address
to be placed into the ARP packet, rendering peers unable to communicate
with the actual destination from which the ARP reply originated.

Load balancing pass-through ARP requests causes an entry to be
created for the peer in the rlb table, and bond_alb_monitor will
occasionally issue ARP updates to all peers in the table instrucing them
as to which MAC address they should communicate with; this occurs when
some event sets rx_ntt.  In the bridged case, however, the MAC address
used for the update would be the MAC of the slave, not the actual source
MAC of the originating destination.  This would render peers unable to
communicate with the destinations beyond the bridge.
Signed-off-by: Zheng Li <zheng.x.li@oracle.com>
Cc: Jay Vosburgh <fubar@us.ibm.com>
Cc: Andy Gospodarek <andy@greyhouse.net>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>