port: fix ring writer buffer overflow

port: fix ring writer buffer overflow

Fixes the buffer overflow that occurs due to following;

1. When the input packet burst does not meet the conditions: (a) being
contiguous (first n bits set in pkts_mask, all the other bits cleared)
and (b) containing a full burst, i.e. at least tx_burst_sz packets
(n >= tx_burst_size). This is the slow(er) code path taken when local
variable expr != 0.
2. There are some packets already in the buffer.
3. The number of packets in the incoming burst (i.e. popcount(pkts_mask))
plus the number of packets already in the buffer exceeds the buffer size
(RTE_PORT_IN_BURST_SIZE_MAX, i.e. 64).

Fixes: bf6931b242f7 ("port: ring")
Fixes: 5f4cd47309d6 ("port: add ring writer nodrop")

Signed-off-by: Jasvinder Singh <jasvinder.singh@intel.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>