ib_pack.h: Fix commentary IBA reference for CNP in IB opcode enum

IBA spec is now 1.3 not 3.1 and vol 1 should be mentioned
as there is also vol 2.

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>