media: net.rst: Fix the level of a section of the net chapter

Due to a mistake, the DVB net chapter was actually broken
into two different chapters. Fix it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/uapi/dvb/net.rst

@@ -28,7 +28,6 @@ header.
 
 .. _net_fcalls:
 
-######################
 DVB net Function Calls
 ######################