i40e: Fix call trace in setup_tx_descriptors

In the Linux kernel, the following vulnerability has been resolved: i40e: Fix call trace in setup_tx_descriptors After PF reset and ethtool -t there was call trace in dmesg sometimes leading to panic. When there was some time, around 5 seconds, between reset and test there were no errors. Problem was that pf reset calls i40e_vsi_close in prep_for_reset and ethtool -t calls i40e_vsi_close in diag_test. If there was not enough time between those commands the second i40e_vsi_close starts before previous i40e_vsi_close was done which leads to crash. Add check to diag_test if pf is in reset and don't start offline tests if it is true. Add netif_info("testing failed") into unhappy path of i40e_diag_test()