net/pcap: fix concurrent multiseg Tx

net/pcap: fix concurrent multiseg Tx

Two cores can send multi segment packets on two different pcap ports.
Because of this, we can't have one single buffer to linearize packets.

Use rte_pktmbuf_read() to copy the packet into a buffer on the stack
and remove eth_pcap_gather_data() when necessary (if the mbuf is
contiguous, rte_pktmbuf_read() just points at the buffer address).

Fixes: 6db141c91e1f ("pcap: support jumbo frames")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>