bfd: Flip the default value of bfd ip source and destination.

This commit flips the default value of bfd ip source and destination,
so that they match the default value of ip destination and source
of vtep schema.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>
bfd: Add configuration for setting and matching mac address.

This commit adds options for configuring the MAC addresses
in BFD state machine.  Therein, the "bfd_local_src_mac" and
"bfd_local_dst_mac" configure the MAC address for transmitted
BFD packets.  The "bfd_remote_dst_mac" configure the matching
of MAC address on received BFD packets.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>