iked: Do not accept superfluous arguments

[Klemens Nanni]

Calling `iked reload' when I meant `ikectl reload' showed that iked
happily returned 0 and and fired up another daemon.

Feedback?

Index: iked.c
===================================================================
RCS file: /cvs/src/sbin/iked/iked.c,v
retrieving revision 1.34
diff -u -p -r1.34 iked.c
--- iked.c      23 Mar 2017 05:29:48 -0000      1.34
+++ iked.c      23 Aug 2017 20:39:12 -0000
@@ -109,6 +109,11 @@ main(int argc, char *argv[])
                        usage();
                }
        }
+       argc -= optind;
+       argv += optind;
+
+       if (argc)
+               usage();
 
        if ((env = calloc(1, sizeof(*env))) == NULL)
                fatal("calloc: env");