nl80211: align path to phy mapping logic with mac80211.sh

nl80211: align path to phy mapping logic with mac80211.sh

The mac80211.sh implementation of the uci "path" option compares the
readlink() results of each /sys/class/ieee80211/*/device link to find
the proper phy directory while iwinfo so far tried to construct a full
path out of the uci value.

The iwinfo approach appears to fail under certain circumstances, e.g.
with Hyper-V systems utilizing PCI passthrough for the radio devices.

This commit mimicks the behaviour of mac80211.sh more closely to
achieve the same results.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>