OpenVPN Release 2.7_rc2

OpenVPN Release 2.7_rc2

version.m4, ChangeLog, Changes.rst

Changes.rst has not received an "2.7_rc2" section - it has the
"highlevel" overview of what is new in 2.7, but for alpha/beta releases
it's better to look at git log to see what has been added/fixed.

Notable changes rc1 -> rc2 are:
    - IPv6 address parsing: fix buffer overread on invalid input
      (CVE-2025-12106)
    - HMAC verification check: fix incorrect memcmp() call
      (CVE-2025-13086)
    - even more type conversion related warnings have been fixed
    - DCO FreeBSD improvements:
        improving debug messages (verb 6)
        implement client-side counter handling
        repair --inactive (and document shortcomings)
        repair handling of DCO disconnection notifications in --client mode
    - Windows/Service improvements, hardening, bugfixes
        fix DNS address list generation (if 3 or more --dns addresses in use)
        fix DNS server undo_list
        disallow "stdin" as config name unless user has OpenVPN admin privs
        fix compilation errors with MSVC v19
        iservice: improve validation of config path (pathcc lib)
           [NOTE: this breaks OpenVPN compatibility with Windows 7]
        tapctl: refactor, improve output, change driver default to ovpn-dco
        iservice: when restoring iface metrics, enforce correct ifindex
    - improve cmocka unit test assert() handling
    - PUSH_UPDATE server: fix reporting of client IPs in ``status`` output
      after pushing a new IPv4/IPv6 address to client
    - AEAD cipher safety margins: fix calculation of AEAD blocks in use
      (old code would undercount blocks)
    - fix invalid pointer creation / memory overread in tls_pre_decrypt
    - deprecate ``--opt-verify`` (change into no-op + warning)

Signed-off-by: Gert Doering <gert@greenie.muc.de>