generic: add some missing kernel config symbols spotted on x86

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34981 3c298f89-4303-0410-b956-a3cf2f4a3e73
iwinfo: replace more wext calls with nl80211 equivalents, attempt to infer nl80211 tx power from debugfs before querying wext

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34982 3c298f89-4303-0410-b956-a3cf2f4a3e73