freeradius2: relax SSL version checks

Merge upstream commit 5ae2a70a135062a025d8fabc104eeae3a2c53a7a to relax the
SSL library version check at runtime.

The objective is to avoid the need for rebuilding freeradius2 whenever we push
binary updates for libopenssl. See https://dev.openwrt.org/ticket/18169 for
reference.

Please backport this change to the for-14.07 branch as well.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>