gve: report 64bit tx_bytes counter from gve_handle_report_stats()

Each tx queue maintains a 64bit counter for bytes, there is
no reason to truncate this to 32bit (or this has not been
documented)

Fixes: 24aeb56f ("gve: Add Gvnic stats AQ command and ethtool show/set-priv-flags.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yangchun Fu <yangchun@google.com>
Cc: Kuo Zhao <kuozhao@google.com>
Cc: David Awogbemila <awogbemila@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>