net/tap: fix mbuf double free when writev fails

net/tap: fix mbuf double free when writev fails

When the tap_write_mbufs() function return with break, mbuf was freed
without increasing num_packets, which could cause applications to free
the mbuf again. And the pmd_tx_burst() function should returns the
number of original packets it actually sent excluding tso mbufs.

Fixes: 9396ad334672 ("net/tap: fix reported number of Tx packets")
Cc: stable@dpdk.org
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>