net/xen-netback: Don't mix hexa and decimal with 0x in the printf format

Append 0x to all %x in order to avoid while reading when there is other
decimal value in the log.

Also replace some of the hexadecimal print to decimal to uniformize the
format with netfront.

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: netdev@vger.kernel.org
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>