net: don't use syscall.NET_RT_IFLISTL on FreeBSD

The golang.org/x/net/route package can't parse the RIB returned
by NET_RT_IFLISTL. Use the route.RIBTypeInterface constant
instead, leaving the choice of syscall up to the route package.

Fixes #48553.

Change-Id: Ida4bd6e332c0dc6dc871d3a93cfb56c0fbc93e1b
Reviewed-on: https://go-review.googlesource.com/c/go/+/353611
Trust: Damien Neil <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: neild

src/net/interface_freebsd.go

@@ -11,16 +11,11 @@ import (
 )
 
 func interfaceMessages(ifindex int) ([]route.Message, error) {
-	typ := route.RIBType(syscall.NET_RT_IFLISTL)
-	rib, err := route.FetchRIB(syscall.AF_UNSPEC, typ, ifindex)
+	rib, err := route.FetchRIB(syscall.AF_UNSPEC, route.RIBTypeInterface, ifindex)
 	if err != nil {
-		typ = route.RIBType(syscall.NET_RT_IFLIST)
-		rib, err = route.FetchRIB(syscall.AF_UNSPEC, typ, ifindex)
-		if err != nil {
-			return nil, err
-		}
+		return nil, err
 	}
-	return route.ParseRIB(typ, rib)
+	return route.ParseRIB(route.RIBTypeInterface, rib)
 }
 
 // interfaceMulticastAddrTable returns addresses for a specific