[PATCH] ieee80211: small ERP handling additions

This adds a flag to the ieee80211_network structure which indicates whether
the stored erp_value is valid (a check against 0 is not enough, since an ERP
of 0 is valid and very meaningful).

I also added the ERP IE bit-definitions to ieee80211.h.

This is needed by some upcoming softmac patches.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>