net/ena: Fix build warning in ena_xdp_set()

This fixes the following build warning in ena_xdp_set(), which is
observed on aarch64 with 64KB page size.

   In file included from ./include/net/inet_sock.h:19,
      from ./include/net/ip.h:27,
      from drivers/net/ethernet/amazon/ena/ena_netdev.c:46:
   drivers/net/ethernet/amazon/ena/ena_netdev.c: In function         \
   ‘ena_xdp_set’:                                                    \
   drivers/net/ethernet/amazon/ena/ena_netdev.c:557:6: warning:      \
   format ‘%lu’                                                      \
   expects argument of type ‘long unsigned int’, but argument 4      \
   has type ‘int’                                                    \
   [-Wformat=] "Failed to set xdp program, the current MTU (%d) is   \
   larger than the maximum allowed MTU (%lu) while xdp is on",

Signed-off-by: Gavin Shan <gshan@redhat.com>
Acked-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>