bond: active-backup mode is using the wrong load balance algo

active-backup mode is using l2 load balance algo. It should be using
active-backup. Also notice that the output is missing a character.

vpp# create bond mode active-backup
create bond mode active-backup
vpp# sh bond
sh bond
interface name   sw_if_index  mode         load balance  active slaves  slaves
BondEthernet0    6            xor          l34           2              2
BondEthernet1    9            xor          l34           1              1
BondEthernet2    10           active-backu l2            0              0
vpp#

Change-Id: If5ed0cc6c25f6c2ddabec15ff6188b34923d38e3
Signed-off-by: Steven <sluong@cisco.com>