Merge in6_pcb.c:1.86 from HEAD to RELENG_6:

Fix leaking MAC labels for IPv6 inpcbs by adding missing MAC label
  destroy call; this transpired because the inpcb alloc path for IPv4/IPv6
  is the same code, but IPv6 has a separate free path.  The results was
  that as new IPv6 TCP connections were created, kernel memory would
  gradually leak.

  Reported by:    tanyong <tanyong at ercist dot iscas dot ac dot cn>,
                  zhouzhouyi

Approved by:	re (kensmith)

sys/netinet6/in6_pcb.c

@@ -65,9 +65,11 @@
 #include "opt_inet.h"
 #include "opt_inet6.h"
 #include "opt_ipsec.h"
+#include "opt_mac.h"
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/mac.h>
 #include <sys/malloc.h>
 #include <sys/mbuf.h>
 #include <sys/domain.h>
@@ -457,6 +459,9 @@ in6_pcbdetach(inp)
 		(void)m_free(inp->inp_options);
 	ip_freemoptions(inp->inp_moptions);
 	inp->inp_vflag = 0;
+#ifdef MAC
+	mac_destroy_inpcb(inp);
+#endif
 	INP_UNLOCK(inp);
 	uma_zfree(ipi->ipi_zone, inp);
 }