mac80211: Various small fixes for cfg.c: mpath_set_pinfo()

Various small fixes for net/mac80211/cfg.c:mpath_set_pinfo():
Initialize *pinfo before filling members in, handle MESH_PATH_RESOLVED
correctly, and remove bogus assignment; result in correct display
of FLAGS values and meaningful EXPTIME for expired paths in iw utility.

Signed-off-by: Yoichi Shinoda <shinoda@jaist.ac.jp>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>