-userv-ipif doesn't like the same bit of network to be specified
-twice. Use the new functionality in ipaddr.c once it's done to prevent
-this.
-
-tun.c: jdamery reports tun-old code works on Linux-2.2.
-Unresolved problem with ioctl(TUNSETIFF) sometimes returning EINVAL, seems
-to be related to early 2.4.x (x<=5) series kernels. 2.4.9 and above seem ok;
-2.4.[678] untested.