PCI/MSI: Move non-mask check back into low level accessors

The recent rework of PCI/MSI[X] masking moved the non-mask checks from the
low level accessors into the higher level mask/unmask functions.

This missed the fact that these accessors can be invoked from other places
as well. The missing checks break XEN-PV which sets pci_msi_ignore_mask and
also violates the virtual MSIX and the msi_attrib.maskbit protections.

Instead of sprinkling checks all over the place, lift them back into the
low level accessor functions. To avoid checking three different conditions
combine them into one property of msi_desc::msi_attrib.

[ josef: Fixed the missed conversion in the core code ]

Fixes: fcacdfbe

 ("PCI/MSI: Provide a new set of mask and unmask functions")
Reported-by: Josef Johansson <josef@oderland.se>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Josef Johansson <josef@oderland.se>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Cc: stable@vger.kernel.org