fix devctl core file name

[aurelien.cazuc.external_stormshield.eu]

Summary

the name of the core file written to the devctl socket is invalid when rotation occurs:
the effective core file is the oldest one, but the name sent to the devctl is the last tested one

in the following situation, files are scanned from test-0.core to test-4.core, but the oldest is test-2.core
the core file will be written to test-2.core, but the devctl will receive test-4.core

-rw-r--r--   1 root wheel  0 Feb 13 14:32 test-0.core
-rw-r--r--   1 root wheel  0 Feb 13 14:32 test-1.core
-rw-r--r--   1 root wheel  0 Feb 13 14:31 test-2.core
-rw-r--r--   1 root wheel  0 Feb 13 14:31 test-3.core
-rw-r--r--   1 root wheel  0 Feb 13 14:31 test-4.core

with the fix, test-2.core will be sent to the devctl socket

Sponsored by: Stormshield

[imp]

sys/kern/kern_sig.c

3881–3882

We can likely drop the (void) cast here and below

3923

I dislike this repetition. It's full of magic and wonder. It's too clever by half, I think, to copy since there's a lot of subtle things going on here. Making it a static inline function seems much safer.