Add DEFAULT_VERSIONS=ssl=XXX

Move the openssl detection routine to bsd.default-version.mk.
Add warnings telling people to not use WITH_OPENSSL_PORT or
WITH_OPENSSL_BASE.

To ease maintainability, change the way the different ssl libraries
version numbers are checked.

PR: 210149
Submitted by: mat
Exp-run by: antoine
Sponsored by: The FreeBSD Foundation, Absolight
Differential Revision: https://reviews.freebsd.org/D6577