mac80211: check ERP info IE length in parser

It's always just one byte, so check for that and
remove the length field from the parser struct.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc net/mac80211/ieee80211_i.h
Simple merge

diff --cc net/mac80211/mlme.c
Simple merge

diff --cc net/mac80211/scan.c
Simple merge

diff --cc net/mac80211/util.c
Simple merge