unix: make Nfgenmsg a type definition

CL 114518 introduced Nfgenmsg as a type alias which breaks the build on
Go <= 1.9. Fix it by making Nfgenmsg a type like all others in
x/sys/unix

Updates golang/go#25561
Fixes golang/go#25563

Change-Id: I9950be857e34e7e3ca79c71fced9663a0cac9b63
Reviewed-on: https://go-review.googlesource.com/114596
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/linux/types.go

@@ -1055,7 +1055,7 @@ const (
 )
 
 // netfilter nfnetlink
-type Nfgenmsg = C.struct_nfgenmsg
+type Nfgenmsg C.struct_nfgenmsg
 
 const (
 	NFNL_BATCH_UNSPEC = C.NFNL_BATCH_UNSPEC

unix/ztypes_linux_386.go

@@ -1382,7 +1382,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_amd64.go

@@ -1402,7 +1402,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_arm.go

@@ -1371,7 +1371,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_arm64.go

@@ -1381,7 +1381,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_mips.go

@@ -1376,7 +1376,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_mips64.go

@@ -1383,7 +1383,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_mips64le.go

@@ -1383,7 +1383,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_mipsle.go

@@ -1376,7 +1376,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_ppc64.go

@@ -1391,7 +1391,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_ppc64le.go

@@ -1391,7 +1391,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16

unix/ztypes_linux_s390x.go

@@ -1408,7 +1408,7 @@ const (
 	NFPROTO_NUMPROTO = 0xd
 )
 
-type Nfgenmsg = struct {
+type Nfgenmsg struct {
 	Nfgen_family uint8
 	Version      uint8
 	Res_id       uint16