[package] mac80211: change wireless ifname numbering schema

[package] mac80211: change wireless ifname numbering schema
Instead of simply counting up until we hit a free iface, group ifnames by wiphy so that the first wlanX on a phy gets the phy number
and following ifaces an index-suffix, e.g. wlan0 for network 1 on phy 1 and wlan0-1 for network 2 on phy 1.
This fixes state var confusion when operating multiple radios and allows to reliably take down and restart one radio only, even if
the number of networks changes in between. This should, along with other changes in LuCI, fix #10335.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@28784 3c298f89-4303-0410-b956-a3cf2f4a3e73