mm, oom: change type of oom_score_adj to short

The maximum oom_score_adj is 1000 and the minimum oom_score_adj is -
1000,
so this range can be represented by the signed short type with no
functional change.  The extra space this frees up in struct
signal_struct
will be used for per-thread oom kill flags in the next patch.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Conflicts:
	drivers/staging/android/lowmemorykiller.c
	include/linux/oom.h
	include/linux/sched.h
	mm/oom_kill.c
	mm/swapfile.c

Conflicts:
	drivers/staging/android/lowmemorykiller.c

Conflicts:

	drivers/staging/android/lowmemorykiller.c