Decode the "LACP Fast Timeout" LAGG option flag

r286700 added the "lacp_fast_timeout" option to `ifconfig', but we forgot to
include the new option in the string used to decode the option bits. Add
"LACP_FAST_TIMO" to LAGG_OPT_BITS.

Also, s/LAGG_OPT_LACP_TIMEOUT/LAGG_OPT_LACP_FAST_TIMO/g , to be clearer that
the flag indicates "Fast Timeout" mode.

Reported by: Greg Foster <gfoster at panasas dot com>
Reviewed by: jpaetzel
MFC after: 1 week
Sponsored by: Panasas
Differential Revision: https://reviews.freebsd.org/D25239