gst1-plugins-bad: add kernel header version dependency on DVB plugin

The DVB plugin uses the FEC_2_5 and QAM_4_NR from the DVB API, which
were added only in kernel 3.7. This commit adds the necessary kernel
header version dependency, which fixes:

  http://autobuild.buildroot.net/results/fab7afc3490d77a6b29760394337298f2fd55d51/



Thanks to Peter Seiderer for the investigation!

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>