Add CTL_PROC back

commit eab03ac7 aka
"[PATCH] Get rid of /proc/sys/proc" was good commit except strace(1) compile
breakage it introduced:

	system.c:1581: error: 'CTL_PROC' undeclared here (not in a function)

So, add dummy enum back.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Cc: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>