xen: netback: use __CONST_RING_SIZE not __RING_SIZE
xen: netback: use __CONST_RING_SIZE not __RING_SIZE

The later causes warnings with gcc 4.5+. __CONST_RING_SIZE was introduced in
667c78afaec0 to fix this but as netback wasn't upstream at the time it did not
benefit, hence:

  CC      drivers/net/xen-netback/netback.o
drivers/net/xen-netback/netback.c:110:37: warning: variably modified 'grant_copy_op' at file scope [enabled by default]
drivers/net/xen-netback/netback.c:111:30: warning: variably modified 'meta' at file scope [enabled by default]
drivers/net/xen-netback/netback.c: In function 'xen_netbk_rx_action':
drivers/net/xen-netback/netback.c:584:6: warning: variable 'irq' set but not used [-Wunused-but-set-variable]

Thanks to Witold Baryluk for pointing this out.

Signed-off-by: Ian Campbell <9be92b3dbbd6611e3e4c9209fb3d04b4919e7cca@citrix.com>
Cc: Witold Baryluk <c1ddf921adec502a27db1660aac1c8f8980224da@smp.if.uj.edu.pl>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas