IB/hfi1: Fix context recovery when PBC has an UnsupportedVL

If a packet stream uses an UnsupportedVL (virtual lane), the send
engine will not send the packet, and it will not indicate that an
error has occurred.  This will cause the packet stream to block.

HFI has 8 virtual lanes available for packet streams.  Each lane can
be enabled or disabled using the UnsupportedVL mask.  If a lane is
disabled, adding a packet to the send context must be disallowed.

The current mask for determining unsupported VLs defaults to 0 (allow
all).  This is incorrect.  Only the VLs that are defined should be
allowed.

Determine which VLs are disabled (mtu == 0), and set the appropriate
unsupported bit in the mask.  The correct mask will allow the send
engine to error on the invalid VL, and error recovery will work
correctly.

Cc: <stable@vger.kernel.org> # 4.9.x+
Fixes: 77241056 ("IB/hfi1: add driver files")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Lukasz Odzioba <lukasz.odzioba@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>