sysrq: add enable_mask in sysrq_moom_op

It is written in the Documentation/sysrq.txt that oom-killer is enabled
when we set "64" in /proc/sys/kernel/sysrq:

<Documentation/sysrq.txt>

Here is the list of possible values in /proc/sys/kernel/sysrq:
64 - enable signalling of processes (term, kill, oom-kill)
^^^^^^^^

but enable_mask is not set in sysrq_moom_op.

Signed-off-by: Naohiro Ooiwa <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/sysrq.c

···
 	.handler	= sysrq_handle_moom,
 	.help_msg	= "Full",
 	.action_msg	= "Manual OOM execution",
+	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
 };
 
 static void sysrq_handle_kill(int key, struct tty_struct *tty)