Send GARP/NA on bonded intf slave up/down if in active-backup mode

Send GARP/NA on bonded intf slave up/down if in active-backup mode

If a bonded interface is in active-backup mode and configured with
IPv4 and/or IPv6 addresses, on slave interface link up/down, send
a GARP packet if configured with an IPv4 address and an unsolcited
NA if configured with an IPv6 address. These packets can help with
faster route convergence in the next hop router/switch.

Change-Id: I68ccb11a4a40cda414704fa08ee0171c952befa2
Signed-off-by: John Lo <loj@cisco.com>