iwlwifi: mvm: debugfs: check length precisely in inject_packet

iwlwifi: mvm: debugfs: check length precisely in inject_packet

When we check the length, we only check that the advertised
data length fits into the data we have, but currently not
that it actually matches correctly.

This should be harmless, but if the first two bytes are zero,
then the iwl_rx_packet_payload_len() ends up negative, and
that might later cause issues if unsigned variables are used,
as this is not something that's normally expected.

Change the validation here to precisely validate the lengths
match, to avoid such issues.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210117164916.5184dfc2a445.I0631d2e4f6ffb93cf06618edb035c45bd6d1d7b9@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>