net: enetc: fix the output issue of 'ethtool --show-ring'

Currently, enetc_get_ringparam() only provides rx_pending and tx_pending,
but 'ethtool --show-ring' no longer displays these fields. Because the
ringparam retrieval path has moved to the new netlink interface, where
rings_fill_reply() emits the *x_pending only if the *x_max_pending values
are non-zero. So rx_max_pending and tx_max_pending to are added to
enetc_get_ringparam() to fix the issue.

Note that the maximum tx/rx ring size of hardware is 64K, but we haven't
added set_ringparam() to make the ring size configurable. To avoid users
mistakenly believing that the ring size can be increased, so set
the *x_max_pending to priv->*x_bd_count.

Fixes: e4a1717b677c ("ethtool: provide ring sizes with RINGS_GET request")
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Link: https://patch.msgid.link/20260320094222.706339-1-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>