ethtool: coalesce: cap profile updates at NET_DIM_PARAMS_NUM_PROFILES

ethtool: coalesce: cap profile updates at NET_DIM_PARAMS_NUM_PROFILES

ethnl_update_profile() walks the ETHTOOL_A_PROFILE_IRQ_MODERATION
nest list with an index 'i' and writes new_profile[i++] without
bounding i. The destination is kmemdup()'d at NET_DIM_PARAMS_NUM_PROFILES
entries (5), but the Netlink nest count is entirely user-controlled.
Netlink policies do not have support for constraining the number
of nested entries (or number of multi-attr entries).

Fixes: f750dfe825b9 ("ethtool: provide customized dim profile management")
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260526153533.2779187-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>