recursive routing: fixes and clean-ups

recursive routing: fixes and clean-ups

 - get rid of atoi() for getting the remote transport port.
 It doesn't change, so no point to do in on every packet.
 In addition, atoi() breaks when we use service names as ports.

 - ensure we correctly handle IPv4 headers with options

 - directly use buf parameter in place of c->c2.buf

GitHub: closes OpenVPN/openvpn#902

Change-Id: I8a0a8029da02fc63adc918e8d98e9f676ff4ea0d
Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1377
Message-Id: <20251114115029.17432-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg34415.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>