RDS/IB: Move tx/rx ring init and refill to later

Since RDS 3.0 and 3.1 have different packet formats,
we need to wait until after protocol negotiation
is complete to layout the rx buffers.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>