xen/pciback: Check PF instead of VF for PCI_COMMAND_MEMORY

xen/pciback: Check PF instead of VF for PCI_COMMAND_MEMORY

Commit 408fb0e5aa7fda0059db282ff58c3b2a4278baa0 (xen/pciback: Don't
allow MSI-X ops if PCI_COMMAND_MEMORY is not set) prevented enabling
MSI-X on passed-through virtual functions, because it checked the VF
for PCI_COMMAND_MEMORY but this is not a valid bit for VFs.

Instead, check the physical function for PCI_COMMAND_MEMORY.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: <stable@vger.kernel.org>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
(cherry picked from commit 8d47065f7d1980dde52abb874b301054f3013602)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
OraBug: 23017418 - Backport Linux v4.4 Xen patches