ethtool: rss: avoid device context leak on reply-build failure

ethtool: rss: avoid device context leak on reply-build failure

We wait with filling the reply for new RSS context creation
until after the driver ->create_rxfh_context call. The driver
needs to fill some of the defaults in the context. The failure
of rss_fill_reply() is somewhat theoretical, but doesn't take
much effort to handle it properly. Call ->remove_rxfh_context().

If the driver's remove callback fails (some implementations like sfc
can return real command errors from firmware RPCs) - skip the xa_erase
and kfree, leaving the context in the xarray. This matches how
ethnl_rss_delete_doit() behaves.

Fixes: a166ab7816c5 ("ethtool: rss: support creating contexts via Netlink")
Link: https://patch.msgid.link/20260522230647.1705600-7-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>