seccomp: split mode setting routines

Separates the two mode setting paths to make things more readable with
fewer #ifdefs within function bodies.

Change-Id: I51d5e734f843d956d298c3acdaba1a3c70d6112e
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Git-commit: 8908dde5a7fdca974374b0dbe6dfb10f69df7216
Git-repo: https://www.codeaurora.org/cgit/external/gigabyte/kernel/msm


Signed-off-by: Ravi Kumar Siddojigari <rsiddoji@codeaurora.org>