dns/dnsmasq-devel: update to v2.92test21

Upstream changes by Simon Kelley:

• 1e83316 2025-08-21 | Formatting. (tag: v2.92test21)
• 9a566c0 2025-08-21 | Tweak recently altered TFTP code.
• 06e2d47 2025-08-21 | Stop lookup_frec() returning old records.
• b52d1d2 2025-08-21 | Tweak get_new_frec() behaviour in "force" mode.
• 18195e7 2025-08-21 | Useful error logging in dhcp-split-relay code.
• d81b1d7 2025-08-21 | Fix TFTP problems with large files.
• 1677c6e 2025-08-20 | More development on dhcp-split-relay. (tag: v2.92test20)

MFH: 2025Q3