vmxnet3: Fix MSI-X/MSI enablement code

This update cleans up the MSI-X/MSI enablement code, fixes
vmxnet3_acquire_msix_vectors() invalid return values and
enables a dead code in case VMXNET3_LINUX_MIN_MSIX_VECT
MSI-X vectors were allocated.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Cc: Shreyas Bhatewara <sbhatewara@vmware.com>
Cc: pv-drivers@vmware.com
Cc: netdev@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>