sysctl: don't print negative flag for proc_douintvec

I saw some very confusing sysctl output on my system:
  # cat /proc/sys/net/core/xfrm_aevent_rseqth
  -2
  # cat /proc/sys/net/core/xfrm_aevent_etime
  -10
  # cat /proc/sys/net/ipv4/tcp_notsent_lowat
  -4294967295

Because we forget to set the *negp flag in proc_douintvec, so it will
become a garbage value.

Since the value related to proc_douintvec is always an unsigned integer,
so we can set *negp to false explictily to fix this issue.

Fixes: e7d316a02f ("sysctl: handle error writing UINT_MAX to u32 fields")
Signed-off-by: Liping Zhang <[email protected]>
Cc: Subash Abhinov Kasiviswanathan <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/sysctl.c

@@ -2136,6 +2136,7 @@ static int do_proc_douintvec_conv(bool *negp, unsigned long *lvalp,
 		*valp = *lvalp;
 	} else {
 		unsigned int val = *valp;
+		*negp = false;
 		*lvalp = (unsigned long)val;
 	}
 	return 0;