It is not common for dvb_net_init to fail, but after the patch
"dvb_net_init: return -errno on error" it can fail due to running out
of memory.  Handle this.

From an audit of dvb_net_init callers.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Reviewed-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>