net/enetc: fix big endian build and buffer allocation

net/enetc: fix big endian build and buffer allocation

There was an error at rte_constant_bswap64 while compiling
with big endian toolchain. so fixing it by adding type cast.

Also, rte_pktmbuf_alloc API should be used to allocate mbuf
instead of rte_pktmbuf_raw_alloc to avoid use of stale mbuf
information.

Fixes: 469c6111a799 ("net/enetc: enable Rx and Tx")
Cc: stable@dpdk.org
Suggested-by: Thomas Monjalon <thomas@monjalon.net>
Signed-off-by: Gagandeep Singh <g.singh@nxp.com>