bond: Add bonding driver and LACP protocol

Add bonding driver to support creation of bond interface which composes of
multiple slave interfaces. The slave interfaces could be physical interfaces,
or just any virtual interfaces. For example, memif interfaces.

The syntax to create a bond interface is
create bond mode <lacp | xor | acitve-backup | broadcast | round-robin>

To enslave an interface to the bond interface,
enslave interface TenGigabitEthernet6/0/0 to BondEthernet0

Please see src/plugins/lacp/lacp_doc.md for more examples and additional
options.

LACP is a control plane protocol which manages and monitors the status of
the slave interfaces. The protocol is part of 802.3ad standard. This patch
implements LACPv1. LACPv2 is not supported.
To enable LACP on the bond interface, specify "mode lacp" when the bond
interface is created. The syntax to enslave a slave interface is the same as
other bonding modes.

Change-Id: I06581d3b87635972f9f0e1ec50b67560fc13e26c
Signed-off-by: Steven <sluong@cisco.com>