dropbear: patch CVE-2025-47203

dropbear: patch CVE-2025-47203

CVE patch [1] as mentioned in [2] relies on several patches not yet
available in version 2020.81 we have in kirkstone.
The good folks from Debian did the hard work identifying them as they
have the same version in bullseye release.
The commits were picked from [3] and they have their references to
dropbear upstream commits.

[1] https://github.com/mkj/dropbear/commit/e5a0ef27c227f7ae69d9a9fec98a056494409b9b
[2] https://security-tracker.debian.org/tracker/CVE-2025-47203
[3] https://salsa.debian.org/debian/dropbear/-/commit/7f48e75892c40cfc6336137d62581d2c4ca7d84c

Signed-off-by: Peter Marko <peter.marko@siemens.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>