shared: fix DNS RR wire cache and EFI boot option bounds checks (#42926)

Invalidate cached DNS RR wire format when
`dns_resource_record_clamp_ttl()` updates `rr->ttl` in place.
Validate each EFI `Boot####` device-path node length before reading
subtype-specific fields.

diff --cc src/resolve/test-dns-rr.c
Simple merge

diff --cc src/shared/dns-rr.c
Simple merge