Change pull request timeout use a timeout rather than a number

Change pull request timeout use a timeout rather than a number

This commit changes the count n_sent_push_requests to time_t based
push_request_timeout. This is more in line to our other timeouts which
are also time based instead of number retries based.

This does not change the behaviour but it prepares allowing to extend
the pull request timeout during a pending authentication. As a user
visible change we print the the time we waited for a timeout instead

Also update the man page to actually document that hand-window controls
this timeout.

Patch V2: grammar fix in manual page

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20210125125628.30364-2-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21490.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>