CLSA-2026-1779437608 dnsmasq: Fix of 5 CVEs

CVE-2026-2291: fix buffer overflow in union bigname - CVE-2026-4890: fix NSEC bitmap parsing infinite loop and OOB reads - CVE-2026-4891: verify rdlen field in RRSIG packets - CVE-2026-4892: fix buffer overflow in helper.c with large CLIDs - CVE-2026-4893: fix broken client subnet validation...