net: don't accept non-left-contiguous netmasks
Summary:
A netmask that contains 1-bits after 0-bits (the 1-bits are not contiguous on the left side) is invalid [1] [2]. The code before this PR used to parse and accept such non-left-contiguous netmasks. However, a coming change that will alter `CNetAddr::ip` to have flexible size would make juggling with such netmasks more difficult, thus drop support for those. [1] https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing#Subnet_masks [2] https://tools.ietf.org/html/rfc4632#section-5.1
Partial backport (1/2) of core PR19628:
https://github.com/bitcoin/bitcoin/pull/19628/commits/1ea57ad67406b3aaaef5254bc2fa7e4134f3a6df
Depends on D9172.
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, majcosta
Reviewed By: #bitcoin_abc, majcosta
Differential Revision: https://reviews.bitcoinabc.org/D9175