Add support for CQE zipping. CQE zipping reduces PCI overhead by
coalescing and zipping multiple CQEs into a single merged CQE. The
feature is enabled by default and can be disabled by a sysctl.

Implementing this feature mlx5_cqwq_pop() has been separated from
mlx5e_get_cqe().

MFC after: 1 week
Submitted by: Mark Bloch <markb@mellanox.com>
Differential Revision: https://reviews.freebsd.org/D4598
Sponsored by: Mellanox Technologies