net: permit Interface with no Name

net: permit Interface with no Name

On darwin the utun interface sometimes has no name.

Fixes #71064

Change-Id: Iec51641880515f8bd3f97bd892c26f68fd588fa3
Reviewed-on: https://go-review.googlesource.com/c/go/+/641855
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Damien Neil <dneil@google.com>