kill dev_ifsioc()

Once upon a time net/socket.c:dev_ifsioc() used to handle SIOCSHWTSTAMP and
SIOCSIFMAP.  These have different native and compat layout, so the format
conversion had been needed.  In 2009 these two cases had been taken out,
turning the rest into a convoluted way to calling sock_do_ioctl().  We copy
compat structure into native one, call sock_do_ioctl() on that and copy
the result back for the in/out ioctls.  No layout transformation anywhere,
so we might as well just call sock_do_ioctl() and skip all the headache with
copying.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>