bonding: bond_xmit_roundrobin() fix

Commit a2fd940f (bonding: fix broken multicast with round-robin mode)
added a problem on litle endian machines.

drivers/net/bonding/bond_main.c:4159: warning: comparison is always
false due to limited range of data type

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>