net: fix build with sparse on L2TPv2 bitfields

net: fix build with sparse on L2TPv2 bitfields

An external project that wants to do additional checks on fields
endianness can remap rte_beXX types to instrumented types and use
sparse.

The current code breaks OVS build with sparse:
../../lib/ofp-packet.c: note: in included file (through
  .../ovs/dpdk-dir/build/include/rte_flow.h, ../../lib/netdev-dpdk.h,
  ../../lib/dp-packet.h):
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:92:37:
  error: invalid bitfield specifier for type restricted ovs_be16.
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:93:37:
  error: invalid bitfield specifier for type restricted ovs_be16.
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:94:40:
  error: invalid bitfield specifier for type restricted ovs_be16.
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:95:37:
  error: invalid bitfield specifier for type restricted ovs_be16.
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:96:40:
  error: invalid bitfield specifier for type restricted ovs_be16.
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:97:37:
  error: invalid bitfield specifier for type restricted ovs_be16.
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:98:37:
  error: invalid bitfield specifier for type restricted ovs_be16.
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:99:40:
  error: invalid bitfield specifier for type restricted ovs_be16.
.../ovs/dpdk-dir/build/include/rte_l2tpv2.h:100:39:
  error: invalid bitfield specifier for type restricted ovs_be16.
make[3]: *** [lib/ofp-packet.lo] Error 1

Use simple uint16_t types for bitfields in L2TPv2 struct.

Fixes: 3a929df1f286 ("ethdev: support L2TPv2 and PPP procotol")
Signed-off-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>