Fix bug when resulted in NXDOMAIN answers instead of NODATA.

check_for_local_domain() was broken due to new code matching F_*
bits in cache entries for DNSSEC. Because F_DNSKEY | F_DS is
used to match RRSIG entries, cache_find_by_name() insists on an exact match
of those bits. So adding F_DS to the bits that check_for_local_domain()
sends to cache_find_by_name() won't result in DS records as well
as the others, it results in only DS records. Add a new bit, F_NSIGMATCH
which suitably changes the behaviour of cache_find_by_name().

src/dnsmasq.h

@@ -440,6 +440,7 @@ struct crec {
 #define F_SECSTAT   (1u<<24)
 #define F_NO_RR     (1u<<25)
 #define F_IPSET     (1u<<26)
+#define F_NSIGMATCH (1u<<27)
 
 /* Values of uid in crecs with F_CONFIG bit set. */
 #define SRC_INTERFACE 0