ixgbe: disallow IPsec Tx offload when in SR-IOV mode

There seems to be a problem in the x540's internal switch wherein if SR-IOV
mode is enabled and an offloaded IPsec packet is sent to a local VF,
the packet is silently dropped.  This might never be a problem as it is
somewhat a corner case, but if someone happens to be using IPsec offload
from the PF to a VF that just happens to get migrated to the local box,
communication will mysteriously fail.

Not good.

A simple way to protect from this is to simply not allow any IPsec offloads
for outgoing packets when num_vfs != 0.  This doesn't help any offloads that
were created before SR-IOV was enabled, but we'll get to that later.
Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_ipsec.c

@@ -693,6 +693,9 @@ static int ixgbe_ipsec_add_sa(struct xfrm_state *xs)
 	} else {
 		struct tx_sa tsa;
 
+		if (adapter->num_vfs)
+			return -EOPNOTSUPP;
+
 		/* find the first unused index */
 		ret = ixgbe_ipsec_find_empty_idx(ipsec, false);
 		if (ret < 0) {