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 <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Florian Lehner <[email protected]>

Author: tklauser

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