Reset DNS_{GETDB_STALEFIRST,DBFIND_STALETIMEOUT} in ns__query_start()

Reset DNS_{GETDB_STALEFIRST,DBFIND_STALETIMEOUT} in ns__query_start()

In case of chained queries (e.g. CNAME) a discrepancy could arise
if the original query had the DNS_GETDB_STALEFIRST bit set, but
the next query doesn't have it (e.g. because the CNAME target is
a authoritative zone for the server) and cause an unanswered query
because of a logic error.

Reset both DNS_GETDB_STALEFIRST and DNS_DBFIND_STALETIMEOUT bits in
the ns__query_start() function before reevaluating whether they are
needed for the current query, and reset them again after calling
the query_lookup() function.