staging/rdma/hfi1: Handle packets with invalid RHF on context 0

Context 0 (which handles the error packets) can potentially receive an invalid
rhf. Hence, it can not depend on RHF sequence number and can only use DMA_RTAIL
mechanism. Detect such packets with invalid rhf using rhf sequence counting
mechanism and drop them.

As DMA_RTAIL mechanism has performance penalties, do not use context 0 for
performance critical verbs path. Use context 0 for VL15 (MAD), multicast and
error packets.

Reviewed-by: Arthur Kepner <arthur.kepner@intel.com>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Dean Luick <dean.luick@intel.com>
Reviewed-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>