V4L/DVB: ir-core: allow specifying multiple protocols at one open/write

With this change, it is now possible to do something like:
        su -c 'echo "none +rc-5 +nec" > /sys/class/rc/rc1/protocols'

This prevents the need of multiple opens, one for each protocol change,
and makes userspace application easier.

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