dropbear: cherry-pick upstream patches

dropbear: cherry-pick upstream patches

critical fixes:
- libtommath: possible integer overflow (CVE-2023-36328)
- implement Strict KEX mode (CVE-2023-48795)

various fixes:
- fix DROPBEAR_DSS and DROPBEAR_RSA config options
- y2038 issues
- remove SO_LINGER socket option
- make banner reading failure non-fatal
- fix "noremotetcp" behavior
- don't try to shutdown a pty
- fix test for multiuser kernels

adds new features:
- option to bind to interface
- allow inetd with non-syslog
- ignore unsupported command line options with dropbearkey

Signed-off-by: Konstantin Demin <[email protected]>
(cherry picked from commit b5cde260487eae86db1661a53e5e5e0823936aab)
[Only add the patches fixing security problems]
Tested-by: Stijn Segers <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/15899
Signed-off-by: Hauke Mehrtens <[email protected]>