[issue35734] ipaddress's _BaseV4._is_valid_netmask fails to detect invalid netmask like 255.254.128.0

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan <tir.karthi at gmail.com>:


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nosy: +xtreak

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35734>
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