Update to v3.18.21 kernel headers.

Change-Id: If068c58cfe6ac29fab76219dbe2eb5b11cf71246
diff --git a/original/uapi/linux/pci_regs.h b/original/uapi/linux/pci_regs.h
index 4a1d0cc..7dd8d80 100644
--- a/original/uapi/linux/pci_regs.h
+++ b/original/uapi/linux/pci_regs.h
@@ -319,6 +319,7 @@
 #define PCI_MSIX_PBA		8	/* Pending Bit Array offset */
 #define  PCI_MSIX_PBA_BIR	0x00000007 /* BAR index */
 #define  PCI_MSIX_PBA_OFFSET	0xfffffff8 /* Offset into specified BAR */
+#define PCI_MSIX_FLAGS_BIRMASK	PCI_MSIX_PBA_BIR /* deprecated */
 #define PCI_CAP_MSIX_SIZEOF	12	/* size of MSIX registers */
 
 /* MSI-X Table entry format */