um: Implement kernel side of SECCOMP based process handling

This adds the kernel side of the seccomp based process handling.

Co-authored-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250602130052.545733-6-benjamin@sipsolutions.net


Signed-off-by: Johannes Berg <johannes.berg@intel.com>