network: fix ip=ibft regression

It looks like ip=ibft has been busted since
  25aa3c5 network: refactor stuff from netroot/parse-ip-opts to net-lib
which moved ibft parsing code out to the ibft_to_cmdline function.

The use of ifname_mac was partially replaced by a local mac, but not
completely, causing ibft_to_cmdline to abort without generating network
configuration options.

Signed-off-by: Chris Leech <cleech@redhat.com>

modules.d/40network/net-lib.sh

@@ -145,8 +145,8 @@ ibft_to_cmdline() {
         for iface in /sys/firmware/ibft/ethernet*; do
             [ -e ${iface}/mac ] || continue
             mac=$(read a < ${iface}/mac; echo $a)
-            [ -z "$ifname_mac" ] && continue
-            dev=$(set_ifname ibft $ifname_mac)
+            [ -z "$mac" ] && continue
+            dev=$(set_ifname ibft $mac)
             dhcp=$(read a < ${iface}/dhcp; echo $a)
             if [ -n "$dhcp" ]; then
                 echo "ip=$dev:dhcp"