RDMA: Mark if create address handle is in a sleepable context

Introduce a 'flags' field to create address handle callback and add a flag
that marks whether the callback is executed in an atomic context or not.

This will allow drivers to wait for completion instead of polling for it
when it is allowed.

Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>