net/cxgb4: use remove handler as shutdown handler

Without a shutdown handler, T4 cards behave very badly after a kexec.
Some firmware calls return errors indicating allocation failures, for
example. This is probably because thouse resources were not released by
a BYE message to the firmware, for example.

Using the remove handler guarantees we will use a well tested path.

With this patch I applied, I managed to use kexec multiple times and
probe and iSCSI login worked every time.
Signed-off-by: NThadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c

@@ -6179,6 +6179,7 @@ static struct pci_driver cxgb4_driver = {
 	.id_table = cxgb4_pci_tbl,
 	.probe    = init_one,
 	.remove   = remove_one,
+	.shutdown = remove_one,
 	.err_handler = &cxgb4_eeh,
 };