expose sendmmsg() syscall in sockets API

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-05-14.17:39:02.060>
labels = ['type-feature', 'library', '3.11']
title = 'expose sendmmsg() syscall  in sockets API'
updated_at = <Date 2022-01-19.15:56:12.577>
user = 'https://github.com/socketpair'

bugs.python.org fields:

activity = <Date 2022-01-19.15:56:12.577>
actor = 'honglei.jiang'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2016-05-14.17:39:02.060>
creator = 'socketpair'
dependencies = []
files = []
hgrepos = []
issue_num = 27022
keywords = []
message_count = 3.0
messages = ['265538', '265733', '410964']
nosy_count = 3.0
nosy_names = ['pitrou', 'honglei.jiang', 'socketpair']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue27022'
versions = ['Python 3.11']