igb_uio: fix build on CentOS 6.8
igb_uio: fix build on CentOS 6.8

Following compile error observed with CentOS 6.8, which uses kernel
kernel-devel-2.6.32-642.el6.x86_64:

In function 'igbuio_msix_mask_irq':
	error: 'PCI_MSIX_ENTRY_CTRL_MASKBIT' undeclared

Reported-by: Thiago Martins <24b1ab6fbdeb4c4fd5c1a0f297b686fd98f7503d@gmail.com>
Signed-off-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk