MPRQ cannot be used in multi-process applications because of
externally attached MPRQ buffers. A callback is registered by
a primary process to free MPRQ buffers once they are no longer
needed. But this information is shared among all the processes.
The virtual address of the mlx5_mprq_buf_free_cb function is
different in a secondary process, which leads to a segmentation
fault. Document that MPRQ is not supported in a multi-process
app, since there is no way to find out if this is the one.
Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com> Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>