plugins/fmcomms2_adv: Scale IQ based on rotation angle

Rotation by 45°, I&Q can be sqrt(2) larger, so scale that we don't overflow
Full Scale

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
plugins/datafile_in.h: Fix sign extension bug and avoid scaling to the max

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Merge branch 'master' of https://github.com/analogdevicesinc/iio-oscilloscope