Make sbuf_copyin() return the number of bytes copied on success.

Submitted by:	"Wojciech A. Koszek" <dunstan@freebsd.czest.pl>

share/man/man9/sbuf.9

@@ -337,6 +337,10 @@ and
 return
 .Dv NULL
 and \-1, respectively, if the buffer overflowed.
+.Pp
+.Fn sbuf_copyin
+returns \-1 if copying string from userland failed, and number of bytes
+copied otherwise.
 .Sh SEE ALSO
 .Xr printf 3 ,
 .Xr strcat 3 ,

sys/kern/subr_sbuf.c

@@ -379,7 +379,7 @@ sbuf_copyin(struct sbuf *s, const void *uaddr, size_t len)
 		return (-1);	/* XXX */
 	}
 
-	return (0);
+	return (done);
 }
 #endif