Add parsing of dhcp-option PROXY_HTTP

Add parsing of dhcp-option PROXY_HTTP

This adds support for setting a HTTP proxy that should be used after
connecting to a VPN.

The syntax has been picked to have compatibility with OpenVPN3.
Otherwise I would have used HTTP-PROXY instead.

Since this option requires an additional argument compared to the
existing dhcp-option keywords, move checking the number of arguments
to the individual keywords.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20210416110955.1162574-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22129.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>