Add blank line after each item in "ngctl ls -l"

The output of "ngctl ls -l" is hard to read. To make it easier, add a blank
line after each listed item much how traditional "ls -l" does when listing
the contents of multiple directories.

Sponsored by:	Smule, Inc.

usr.sbin/ngctl/list.c

@@ -125,6 +125,8 @@ ListCmd(int ac, char **av)
 				break;
 			ninfo++;
 			nlist->numnames--;
+			if (nlist->numnames > 0)
+				printf("\n");
 		}
 	} else {
 		while (nlist->numnames > 0) {