expose per port information via kstats.

expose per port information via kstats.

the most interesting information exposed here is the number of times
a port changes state according to the lacp state machine. if a port
is flapping, it's hard to see if you only look at the current state.
getting a count of changes over time makes problems a lot more
visible and therefore fixable.

this also exposes counters around how the lacp protocol packets.
all of these can be useful when trying to line up behaviors with
another system (eg, a switch).

ok jmatthew@