IB: Fix modify QP checking of "current QP state" attribute

According to the IB spec version 1.2, section 11.2.4.2, the current
table has a couple of mistakes where it allows the current QP state
(IB_QP_CUR_STATE) attribute.  For the transitions:

  RTS -> RTS: IB_QP_CUR_STATE should be allowed for all transports
  SQD -> SQD: IB_QP_CUR_STATE should never be allowed

Signed-off-by: Dotan Barak <dotanb@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>