net: stmmac: Fix queue statistics reading

net: stmmac: Fix queue statistics reading

Correct queue statistics reading. All queue statistics are stored as unsigned
long values. The retrieval for ethtool fetches these values as u64. However, on
some systems the size of the counters are 32 bit. That yields wrong queue
statistic counters e.g., on arm32 systems such as the stm32mp157. Fix it by
using the correct data type.

Tested on Olimex STMP157-OLinuXino-LIME2 by simple running linuxptp for a short
period of time:

Non-patched kernel:
|root@st1:~# ethtool -S eth0 | grep q0
|     q0_tx_pkt_n: 3775276254951 # ???
|     q0_tx_irq_n: 879
|     q0_rx_pkt_n: 1194000908909 # ???
|     q0_rx_irq_n: 278

Patched kernel:
|root@st1:~# ethtool -S eth0 | grep q0
|     q0_tx_pkt_n: 2434
|     q0_tx_irq_n: 1274
|     q0_rx_pkt_n: 1604
|     q0_rx_irq_n: 846

Fixes: 68e9c5dee1cf ("net: stmmac: add ethtool per-queue statistic framework")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Cc: Vijayakannan Ayyathurai <vijayakannan.ayyathurai@intel.com>
Cc: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>