sfc: fix considering that all channels have TX queues

Normally, all channels have RX and TX queues, but this is not true if
modparam efx_separate_tx_channels=1 is used. In that cases, some
channels only have RX queues and others only TX queues (or more
preciselly, they have them allocated, but not initialized).

Fix efx_channel_has_tx_queues to return the correct value for this case
too.

Messages shown at probe time before the fix:
 sfc 0000:03:00.0 ens6f0np0: MC command 0x82 inlen 544 failed rc=-22 (raw=0) arg=0
 ------------[ cut here ]------------
 netdevice: ens6f0np0: failed to initialise TXQ -1
 WARNING: CPU: 1 PID: 626 at drivers/net/ethernet/sfc/ef10.c:2393 efx_ef10_tx_init+0x201/0x300 [sfc]
 [...] stripped
 RIP: 0010:efx_ef10_tx_init+0x201/0x300 [sfc]
 [...] stripped
 Call Trace:
  efx_init_tx_queue+0xaa/0xf0 [sfc]
  efx_start_channels+0x49/0x120 [sfc]
  efx_start_all+0x1f8/0x430 [sfc]
  efx_net_open+0x5a/0xe0 [sfc]
  __dev_open+0xd0/0x190
  __dev_change_flags+0x1b3/0x220
  dev_change_flags+0x21/0x60
 [...] stripped

Messages shown at remove time before the fix:
 sfc 0000:03:00.0 ens6f0np0: failed to flush 10 queues
 sfc 0000:03:00.0 ens6f0np0: failed to flush queues

Fixes: 8700aff0 ("sfc: fix channel allocation with brute force")
Reported-by: Tianhao Zhao <tizhao@redhat.com>
Signed-off-by: Martin Habets <habetsm.xilinx@gmail.com>
Tested-by: Íñigo Huguet <ihuguet@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/net_driver.h

@@ -1530,7 +1530,7 @@ static inline bool efx_channel_is_xdp_tx(struct efx_channel *channel)
 
 static inline bool efx_channel_has_tx_queues(struct efx_channel *channel)
 {
-	return true;
+	return channel && channel->channel >= channel->efx->tx_channel_offset;
 }
 
 static inline unsigned int efx_channel_num_tx_queues(struct efx_channel *channel)