[NET] tun/tap: fixed hw address handling

Fixed tun/tap driver's handling of hw addresses.  The hw address is stored
in both the net_device.dev_addr and tun.dev_addr fields.  These fields were
not kept synchronized, and in fact weren't even initialized to the same
value.  Now during both init and when performing SIOCSIFHWADDR on the tun
device these values are both updated.  However, if SIOCSIFHWADDR is
performed on the net device directly (for instance, setting the hw address
using ifconfig), the tun device does not get updated.  Perhaps the
tun.dev_addr field should be removed completely at some point, as it is
redundant and net_device.dev_addr can be used anywhere it is used.

Signed-off-by: Brian Braunstein <linuxkernel@bristyle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>