Implement IPv6 in TUN mode for Windows TAP driver.

Implement IPv6 in TUN mode for Windows TAP driver.

* install-win32/settings.in: bump version to 9.7, TAP_RELDATE to "07/03/2010".

* tap-win32/proto.h: add data types and definitions needed for IPv6

* tap-win32/types.h: add m_UserToTap_IPv6 ethernet header for IPv6 packets

* tap-win32/tapdrvr.c: implement support for IPv6 in TUN mode:
     - IPv6 packets User->OS need correct ether type
     - IPv6 packets OS->User get correctly forwarded
     - IPv6 neighbour discovery packets for "fe80::8" (magic address
       installed as route-nexthop by OpenVPN.exe) get answered locally
(cherry picked from commit 175e17a5abd5969f6803a9cc9587b7959e1100ae)

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>