Check that the alternate P_Key index is in range when setting the
alternate path for a QP.  Also make a cosmetic touch up to the debug
message printed when the main P_Key index is out of range.
Signed-off-by: NDotan Barak <dotanb@mellanox.co.il>
Signed-off-by: NRoland Dreier <rolandd@cisco.com>