bonding: add and use bond_is_lb()

Introduce and use bond_is_lb(), it is usefull to shorten the repetitive
check for either ALB or TLB mode.

Signed-off-by: Holger Eitzenberger <holger@eitzenberger.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc drivers/net/bonding/bond_main.c
Simple merge

diff --cc drivers/net/bonding/bonding.h
Simple merge