net: reject leading zeros in IP address parsers

net: reject leading zeros in IP address parsers

In both net.ParseIP and net.ParseCIDR reject leading zeros in the
dot-decimal notation of IPv4 addresses.

Fixes #30999
Fixes #43389

Change-Id: I2b6a31fe84db89ac828cf5ed03eaa586ee96ab68
Reviewed-on: https://go-review.googlesource.com/c/go/+/325829
Trust: Roland Shoemaker <roland@golang.org>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>