Revert "route: remove unused sizeof* consts on freebsd"

This reverts CL 633155.

Reason for revert: This is part of a short chain of CLs that causes
x/net to depend on x/sys. We have a policy that prevents us from
vendoring x/sys into std, but x/net needs to be vendored.

Change-Id: Ib773f21dee59fe6f4afb7ba1d7ae01d8859110c6
Reviewed-on: https://go-review.googlesource.com/c/net/+/634255
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: mknyszek

route/defs_freebsd.go

@@ -227,6 +227,12 @@ const (
 	sizeofIfMsghdrFreeBSD10 = C.sizeof_struct_if_msghdr_freebsd10
 	sizeofIfMsghdrFreeBSD11 = C.sizeof_struct_if_msghdr_freebsd11
 
+	sizeofIfDataFreeBSD7  = C.sizeof_struct_if_data_freebsd7
+	sizeofIfDataFreeBSD8  = C.sizeof_struct_if_data_freebsd8
+	sizeofIfDataFreeBSD9  = C.sizeof_struct_if_data_freebsd9
+	sizeofIfDataFreeBSD10 = C.sizeof_struct_if_data_freebsd10
+	sizeofIfDataFreeBSD11 = C.sizeof_struct_if_data_freebsd11
+
 	sizeofRtMsghdrFreeBSD10Emu  = C.sizeof_struct_rt_msghdr
 	sizeofRtMetricsFreeBSD10Emu = C.sizeof_struct_rt_metrics
 
@@ -235,4 +241,14 @@ const (
 	sizeofIfMsghdrFreeBSD9Emu  = C.sizeof_struct_if_msghdr_freebsd9
 	sizeofIfMsghdrFreeBSD10Emu = C.sizeof_struct_if_msghdr_freebsd10
 	sizeofIfMsghdrFreeBSD11Emu = C.sizeof_struct_if_msghdr_freebsd11
+
+	sizeofIfDataFreeBSD7Emu  = C.sizeof_struct_if_data_freebsd7
+	sizeofIfDataFreeBSD8Emu  = C.sizeof_struct_if_data_freebsd8
+	sizeofIfDataFreeBSD9Emu  = C.sizeof_struct_if_data_freebsd9
+	sizeofIfDataFreeBSD10Emu = C.sizeof_struct_if_data_freebsd10
+	sizeofIfDataFreeBSD11Emu = C.sizeof_struct_if_data_freebsd11
+
+	sizeofSockaddrStorage = C.sizeof_struct_sockaddr_storage
+	sizeofSockaddrInet    = C.sizeof_struct_sockaddr_in
+	sizeofSockaddrInet6   = C.sizeof_struct_sockaddr_in6
 )