mail/fetchmail: backport SNI support from upstream

This affects some servers such as Gmail.

See also bugs on Linux distributions.

• https://bugzilla.redhat.com/show_bug.cgi?id=1611815
• https://bugs.launchpad.net/ubuntu/+source/fetchmail/+bug/1798786

PR: 233078
Submitted by: fuyuhiko.maruyama@gmail.com
Approved by: Corey Halpin <chalpin@cs.wisc.edu> (maintainer), mentors (implicit)
Obtained from: https://gitlab.com/fetchmail/fetchmail/commit/9b8b634312f169fab872f3580c2febe5af031615
MFH: 2018Q4