Add security advisories affecting 14.3R, 14.4R and 15.0R

FreeBSD-SA-26:25.thr affects all supported releases
FreeBSD-SA-26:26.ktls affects all supported releases
FreeBSD-SA-26:27.sound affects all supported releases
FreeBSD-SA-26:28.capsicum affects all supported releases
FreeBSD-SA-26:29.ip6_multicast affects all supported releases
FreeBSD-SA-26:30.linux affects all supported releases
FreeBSD-SA-26:31.arm64 affects all supported releases
FreeBSD-SA-26:32.elf affects all supported releases
FreeBSD-SA-26:33.unbound affects all supported releases
FreeBSD-SA-26:34.vt affects all supported releases
FreeBSD-SA-26:35.openssl affects all supported releases
FreeBSD-SA-26:36.ldns affects all supported releases