netinet: Add a sysctl to allow disabling connections to INADDR_ANY
See the discussion in Bugzilla PR 280705 for context.
PR: 280705
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D46259
(cherry picked from commit 417b35a97b7669eb0bf417b43e97cccbedbce6f9)