igb_uio: fix build with long term kernel and RHEL

igb_uio: fix build with long term kernel and RHEL

Function pci_num_vf() is introduced from upstream linux-2.6.34. So
this patch make compatible with longterm kernel linux-2.6.32.63.

For RHEL, function pci_num_vf() begins from RHEL5 update9. And
it is stub-defined when CONFIG_PCI_IOV is not enabled.

So dropped the CONFIG_PCI_IOV checking of commit 11ba0426.

For other distro like RHEL behaved to pci_num_vf(), we could simply
append following condition macro:
(!(defined(OTHER_RELEASE_CODE) && \
 OTHER_RELEASE_CODE >= OTHER_RELEASE_VERSION(X, Y)))

Signed-off-by: Jincheng Miao <jmiao@redhat.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>