[media] dvb-net: Fix probable mask then right shift defects

Precedence of & and >> is not the same and is not left to right.
shift has higher precedence and should be done after the mask.

Add parentheses around the mask.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>