Check TF_TOE not the tod pointer to determine if TOE is active.

[jhb]

Summary

The TF_TOE flag is the check used in the rest of the network stack to
determine if TOE is active on a socket. There is at least one path in
the cxgbe(4) TOE driver that can leave the tod pointer non-NULL on a
socket not using TOE.

Test Plan

• found by Chelsio QA, was not able to reproduce myself, but this seems like the right fix