Indicate that a client is in pull mode in IV_PROTO

Indicate that a client is in pull mode in IV_PROTO

This allows us to skip waiting for the first PUSH_REQUEST message from
the client to send the response.

This changes the interpretation of IV_PROTO from a scalar to a bitfield
Since we only have IV_PROTO=2 defined so far and will support DATA_V2
this should not make any problem. This avoid adding another IV_xxx variable
that takes valuable space in the protocol frame.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Patch V2: Use bitmask for IV_PROTO_DATA_V2 and add more documentation.

Patch V3: Rewrite IV_PROTO paragraph in man page, incoperate spelling fixes
          by Richard Bonhomme <tincanteksup@gmail.com>

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20200721163811.22745-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20525.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>