ipv6: support attaching packet filters to PacketConn.

Fixes golang/go#14974

Change-Id: I58c41acf29329aedf61b9ca59eb271e4536c80ea
Reviewed-on: https://go-review.googlesource.com/23107
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>
diff --git a/ipv6/zsys_linux_mips64.go b/ipv6/zsys_linux_mips64.go
index ec8ce15..141c869 100644
--- a/ipv6/zsys_linux_mips64.go
+++ b/ipv6/zsys_linux_mips64.go
@@ -86,6 +86,9 @@
 	sysICMPV6_FILTER_BLOCKOTHERS = 0x3
 	sysICMPV6_FILTER_PASSONLY    = 0x4
 
+	sysSOL_SOCKET       = 0x1
+	sysSO_ATTACH_FILTER = 0x1a
+
 	sysSizeofKernelSockaddrStorage = 0x80
 	sysSizeofSockaddrInet6         = 0x1c
 	sysSizeofInet6Pktinfo          = 0x14
@@ -154,3 +157,16 @@
 type sysICMPv6Filter struct {
 	Data [8]uint32
 }
+
+type sysSockFProg struct {
+	Len       uint16
+	Pad_cgo_0 [6]byte
+	Filter    *sysSockFilter
+}
+
+type sysSockFilter struct {
+	Code uint16
+	Jt   uint8
+	Jf   uint8
+	K    uint32
+}