net: adjust the test for IPv4 loopback address block
net: adjust the test for IPv4 loopback address block

We live in the era of virtualization and isolation.
There is no reason to hesitate to use IPv4 loopback address block for
umbrella-type customer accommodating services.

Fixes #23903

Change-Id: I990dd98e2651a993dac1b105c0bc771f8631cb93
Reviewed-on: https://go-review.googlesource.com/95336
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

nawawi/go,josharian/go,nawawi/go,josharian/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,akutz/go,cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,codestation/go,akutz/go,golang/go,akutz/go,codestation/go,cloudflare/go,nawawi/go,golang/go,nawawi/go,josharian/go,Cofyc/go,Cofyc/go,codestation/go,codestation/go,golang/go,akutz/go,cloudflare/go,cloudflare/go,akutz/go,nawawi/go,cloudflare/go,josharian/go,nawawi/go,Cofyc/go,akutz/go,codestation/go,cloudflare/go,Cofyc/go,CAFxX/go,josharian/go,Cofyc/go,codestation/go,nawawi/go,Cofyc/go,Cofyc/go,josharian/go,nawawi/go,akutz/go,akutz/go,josharian/go,golang/go,golang/go,golang/go,codestation/go,golang/go,Cofyc/go,cloudflare/go,josharian/go,codestation/go,CAFxX/go