net: dns: Do not pass 0 as TTL or hop limit

We specifically set TTL/hoplimit to 1 for LLMNR,
but only want to set it if in that specific case.
We must not pass TTL/hoplimit value 0 as that would
cause the packet to be dropped.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>