Cleanup route error and debug logging on Windows

Cleanup route error and debug logging on Windows

Use a unified logging format for various route-methods

- Route add/delete errors are always logged with M_WARN, so
  log only additional information (succeed/exists) with D_ROUTE.

- Non-windows platforms log route errors with a prefix "ERROR:" and
  debug info with "ROUTE:". Do the same on Windows. Do not log
  errors or success multiple times.

- In add_route_ipv6, log the interface id instead of device name
  as the latter always point to the tun/tap adapter name on Windows.

Log lines prefixed with a PACKAGE_NAME "ROUTE" are unchanged.
They appear to use the same format on all platforms.

v2: rebase to master

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20230120094100.2063883-1-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26058.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>