Fix -Wunused warnings, bump WARNS to 6

The output is still broken if prove -rv is run and the testcase aborts
prematurely with fail_assertion (the testcase doesn't really conform to TAP
protocol properly, except when it completes fully)

MFC after: 1 week
Sponsored by: EMC / Isilon Storage Division

tools/regression/sockets/kqueue/Makefile

@@ -4,5 +4,6 @@
 
 PROG=	kqueue
 MAN=
+WARNS?=	6
 
 .include <bsd.prog.mk>

tools/regression/sockets/kqueue/kqueue.c

@@ -250,9 +250,9 @@ test_evfilt_write(int kq, int fd[2], const char *socktype)
  * sockets, and confirm that we can register for various events on them.
  */
 int
-main(int argc, char *argv[])
+main(void)
 {
-	int i, kq, sv[2];
+	int kq, sv[2];
 
 	printf("1..49\n");