vfio: do not needlessly setup device in secondary process

vfio: do not needlessly setup device in secondary process

Setting up a device that wasn't setup in the primary
process will possibly break the primary process. That's
because the IPC message to retrieve the group fd in the
primary will also *open* that group if it wasn't opened
before. Even though the secondary process closes that fd
soon after as a part of its error handling path, the
primary process leaks it.

What's worse, opening that fd on the primary will
increment the process-local counter of opened groups.
If it was 0 before, then the group will never be added
to the vfio container, nor dpdk memory will be ever
mapped.

This patch moves the proper error checks earlier in the
code to fully prevent setting up devices in secondary
processes that weren't setup in the primary process.

Fixes: 2f4adfad0a69 ("vfio: add multiprocess support")

Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>