vfio: share default container in multi-process

vfio: share default container in multi-process

So far each process in MP used to have a separate container
and relied on the primary process to register all memsegs.

Mapping external memory via rte_vfio_container_dma_map()
in secondary processes was broken, because the default
(process-local) container had no groups bound. There was
even no way to bind any groups to it, because the container
fd was deeply encapsulated within EAL.

This patch introduces a new SOCKET_REQ_DEFAULT_CONTAINER
message type for MP synchronization, makes all processes
within a MP party use a single default container, and hence
fixes rte_vfio_container_dma_map() for secondary processes.

From what I checked this behavior was always the same, but
started to be invalid/insufficient once mapping external
memory was allowed.

While here, fix up the comment on rte_vfio_get_container_fd().
This function always opens a new container, never reuses
an old one.

Fixes: 73a639085938 ("vfio: allow to map other memory regions")
Cc: stable@dpdk.org
Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>