IB/hfi1: Add mtu check for operational data VLs

Since Virtual Lanes BCT credits and MTU are set through separate MADs, we
have to ensure both are valid, and data VLs are ready for transmission
before we allow port transition to Armed state.

Fixes: 5e2d6764 ("IB/hfi1: Verify port data VLs credits on transition to Armed")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Alex Estrin <alex.estrin@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>