o Allow non-root users to open /dev/tun* (remove suser()

in tunopen())

o Change the default device permissions to 0600 root:wheel

(were uucp:dialer)

o Only let root (suser()) change the MTU

This makes it possible for an administrator to open up the
permissions on /dev/tun*, letting non-root programs service
a tun interface. Co-operation is still required with a
priviledged program that will configure the interface side
of things.