FreeBSD networking cleanup

FreeBSD networking cleanup

Address a few minor code review remarks:

 - use constants for the inet_ntop() buffers
 - replace argv_printf() + argv_printf_cat() with a single argv_printf()
 - net_route_v4/6 both add and remove, so adjust the error message to
   reflect that.

Signed-off-by: Kristof Provost <kprovost@netgate.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20220822092834.14231-2-kprovost@netgate.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25054.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>