wifi: Fix tethering with kernel 3.5

wifi: Fix tethering with kernel 3.5

Wifi tethering works with kernel 3.4, but not with 3.5. Bisecting
showed that the following kernel patch causes the breakage:
    "3edaf3e mac80211: manage AP netdev carrier state".

Running connman with debugging enabled showed that in case of 3.4
we have the following sequence of RTM_NEWLINK events from the kernel:

1. IFF_UP not set, ifi_change=1
2. IFF_UP,IFF_LOWER_UP, ifi_change=1

which makes connman do the following:

connmand[210]: plugins/wifi.c:wifi_newlink() index 4 flags 4098 change 1
connmand[210]: plugins/wifi.c:wifi_newlink() interface down
connmand[210]: plugins/wifi.c:wifi_newlink() index 4 flags 69635 change 1
connmand[210]: plugins/wifi.c:wifi_newlink() interface up
connmand[210]: plugins/wifi.c:wifi_newlink() carrier on
connmand[210]: plugins/wifi.c:handle_tethering() index 4 bridge tether

However, in 3.5 we have the following sequents of events from the kernel:

1. IFF_UP, ifi_change=1
2. IFF_UP,IFF_LOWER_UP, ifi_change=0

which makes connman do the following:

connmand[493]: plugins/wifi.c:wifi_newlink() index 4 flags 4099 change 1
connmand[493]: plugins/wifi.c:wifi_newlink() interface up
connmand[493]: plugins/wifi.c:wifi_newlink() index 4 flags 69635 change 0

The root-cause for it is that connman handles the "ifi_change" flag
incorrectly. Connman interprets it as "if non-zero, there was some change",
which is wrong. According to RFC 3549, it is "reserved for future use.
Must be set to 0xFFFFFFFF". Thus, just remove that check, which makes
tethering work.