unix: add SizeofNhmsg and SizeofNexthopGrp

These were missed in CL 227357.

For golang/go#38249

Change-Id: Iab75145ae77a027e11bc4cad75300af0a510a537
Reviewed-on: https://go-review.googlesource.com/c/sys/+/716780
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Florian Lehner <lehner.florian86@gmail.com>

unix/linux/types.go

@@ -3600,8 +3600,12 @@ type FsverityEnableArg C.struct_fsverity_enable_arg
 
 type Nhmsg C.struct_nhmsg
 
+const SizeofNhmsg = C.sizeof_struct_nhmsg
+
 type NexthopGrp C.struct_nexthop_grp
 
+const SizeofNexthopGrp = C.sizeof_struct_nexthop_grp
+
 const (
 	NHA_UNSPEC     = C.NHA_UNSPEC
 	NHA_ID         = C.NHA_ID

unix/ztypes_linux.go

@@ -3590,6 +3590,8 @@ type Nhmsg struct {
 	Flags    uint32
 }
 
+const SizeofNhmsg = 0x8
+
 type NexthopGrp struct {
 	Id     uint32
 	Weight uint8
@@ -3597,6 +3599,8 @@ type NexthopGrp struct {
 	Resvd2 uint16
 }
 
+const SizeofNexthopGrp = 0x8
+
 const (
 	NHA_UNSPEC     = 0x0
 	NHA_ID         = 0x1