Fix -Wunused warnings, bump WARNS to 6

The testcase fails today on subtest # 9

The output is still broken if prove -rv is run and the testcase aborts
prematurely (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/accf_data_attach/Makefile

@@ -4,8 +4,6 @@
 
 PROG=	accf_data_attach
 MAN=
-
-accf_data_attach: accf_data_attach.c
-	gcc -Wall -o accf_data_attach accf_data_attach.c
+WARNS?=	6
 
 .include <bsd.prog.mk>

tools/regression/sockets/accf_data_attach/accf_data_attach.c

@@ -58,7 +58,7 @@
  *   make sure it is removed.
  */
 int
-main(int argc, char *argv[])
+main(void)
 {
 	struct accept_filter_arg afa;
 	struct sockaddr_in sin;