[package] hostapd,madwifi: rename agmode option to hwmode. 11a and 11g aren't...

[package] hostapd,madwifi: rename agmode option to hwmode. 11a and 11g aren't the only allowed values

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@13790 3c298f89-4303-0410-b956-a3cf2f4a3e73