lacp: New command "lacp/show-stats" fordisplaying LACP counters.

lacp: New command "lacp/show-stats" fordisplaying LACP counters.

Currently OVS does not provide any command to display stats for LACP
without which it is difficult to debug LACP issues. Here we propose
to display various statistics about LACP PDUs and slave state change.

Sample output:

ovs_lacp # ovs-appctl lacp/stats-show
---- bond-prv statistics ----

slave: dpdk0:
        RX PDUs: 128
        RX Bad PDUs: 0
        TX PDUs: 5
        Link Expired: 2
        Link Defaulted: 1
        Carrier Status Changed: 0

Signed-off-by: Nitin Katiyar <nitin.katiyar@ericsson.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>