iwlwifi: mvm: dump frames early on invalid rate

Currently when rate isn't found (invalid rate or CCK rate in high
band) driver is assigning rate -1, which causes mac80211 to dump
it later with the cryptic rate value of 0xFF.
Instead, warn early and dump the frame in mvm.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>