dns: Use ntohl for ans->ttl in dns_parse_answer_ex

dns_parse_answer_ex was not converting ans->ttl from network
by order to host byte order which was causing certain ttls
it to go negative. In turn this was causing answer edit checks
to fail.

ASTERISK-25528 #close
Reported-by: Daniel Tryba
Tested-by: George Joseph

Change-Id: I31505132d6321c46d2f39fd06c20ee808a864037