net: socket: return changed ifreq from SIOCDEVPRIVATE

Some drivers that use SIOCDEVPRIVATE ioctl commands modify
the ifreq structure and expect it to be passed back to user
space, which has never really happened for compat mode
because the calling these drivers through ndo_do_ioctl
requires overwriting the ifr_data pointer.

Now that all drivers are converted to ndo_siocdevprivate,
change it to handle this correctly in both compat and
native mode.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>