dpdk-ipsec: fix encrypt/decrypt single queue

dpdk-ipsec: fix encrypt/decrypt single queue

When the same worker thread processes packet for encrypt and decrypt,
ie. single worker with bi-directional traffic, given that the queue is
shared results in packets to be decrypted being dropped as the encrypt
always happens first for each main loop.

With this change, each crypto device queue is logically split into two
queues, each half the real size, avoiding the described problem.

Change-Id: Ifd3f15e316c92fbd6ca05802456b10a7f73f85da
Signed-off-by: Sergio Gonzalez Monroy <sgmonroy@gmail.com>