The current implementation uses "relative" WDF timers
which are "not ticked" at low power states and on resume
they continue to where they were left of. This makes keepalive
timeout detection sub-optimal, since in worst case a client
has to wait for "ping-restart" seconds to reconnect, which could
be several minutes.

Refactor timers in a way that we only have single timer ticking
every second. At that tick we compare "last" and "now" timestamps
and do actions, similar to what openvpn2 is doing.

Fixes https://github.com/OpenVPN/ovpn-dco-win/issues/64

Signed-off-by: Lev Stipakov <lev@openvpn.net>