ip_interface addition and subtraction changes netmask

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-11-26.23:14:01.991>
labels = ['type-bug', 'library', '3.10']
title = 'ip_interface addition and subtraction changes netmask'
updated_at = <Date 2020-11-28.20:04:31.585>
user = 'https://bugs.python.org/wykoterhaar'

bugs.python.org fields:

activity = <Date 2020-11-28.20:04:31.585>
actor = 'epaine'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-11-26.23:14:01.991>
creator = 'wyko.ter.haar'
dependencies = []
files = []
hgrepos = []
issue_num = 42477
keywords = []
message_count = 1.0
messages = ['381918']
nosy_count = 2.0
nosy_names = ['pmoody', 'wyko.ter.haar']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42477'
versions = ['Python 3.10']