Adds security quick-fix to avoid an open 'OpenWrt' WLAN after an update.

For an so far unknown reason one of the nodes in the testing stream had
an additional open WLAN called 'OpenWrt' after updating from v0.5.3 to
v0.6.0~rc2. It has to be mentioned, though, that this node used a
heavily customized network configuration prior to the update to fullfil
some very specific needs.

It should however be avoided that a new network suddenly appears after
applying an update in any case. As a cause for this, the mac80211.sh
located in '/lib/wifi/' has been identified, which scans for unknown
PHYs when executed and adds them along with such an example network to
'/etc/config/wireless'. For a pure OpenWRT router this behaviour is not
that much a problem, as the radio itself gets deactivated by adding an
"option disabled '1'" that must be removed manually by a user. In comb-
ination with Gluon this becomes critical, as the gluon-mesh-batman-adv-
core package would enable the radio automatically, such that a node can
connect to other Freifunk nodes over WiFi. Generally, a network
'OpenWrt' should not exist anymore in '/etc/config/wireless' by that
time. The reason for which in the case mentioned above there was such
an entry is still unknown.

In order to exclude such a security risk, for now we provide a modified
copy of '/lib/wifi/mac802111.sh' with this packages, in which the
corresponding lines to add a default/example network 'OpenWrt' have been
removed compeletely. This modified version of the script replaces the
original script at build-time.

Signed-off-by: Stefan Laudemann <thisco@webcake.de>