i9300: fix 2g/3g toggle

If we're trying to set network mode 0, modem always responds with network mode 7 which causes
the upper
layer to set network mode 0 again. This results in a never ending loop of setting 0 and getting
7.
If we're getting mode 7 we'll rewrite it to mode 0 and everyone is happy.

Change-Id: Ibff9e9162589135350dd2c4b3fb392ef64d95e4a