media: em28xx: explicitly disable TS packet filter

The em28xx driver never touched the EM2874 register bits that control
the transport stream packet filters, leaving them at whatever default
the firmware has set. E.g. the Pinnacle 290e disables them by default,
while the Hauppauge WinTV dualHD enables discarding NULL packets by
default.

However, some applications require NULL packets, e.g. to determine the
load in DOCSIS segments, so discarding NULL packets is undesired for
such applications.

This patch simply extends the bit mask when starting or stopping the
transport stream packet capture, so that the filter bits are cleared.
It has been verified that this makes the Hauppauge WinTV dualHD pass
an unfiltered DVB-C stream including NULL packets, which it didn't
before.

Signed-off-by: Robert Schlabbach <Robert.Schlabbach@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>