Some imon devices (like 15c2:0036) need a higher delay between
send_packet calls.

Default value is still 5ms to avoid regressions on already working
hardware.

Also use interruptible wait to avoid load average going too high (and
let caller handle signals).
Signed-off-by: Kevin Baradon <kevin.baradon@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>