iwlwifi: pcie: skip fragmented receive buffers

We don't really expect fragmented RBs, and don't seem to be seeing
them in practice since that would've caused a crash. Nevertheless,
we should be expecting the hardware to send them.

Parse the flag indicating a fragmented buffer, but then discard it
and any fragments thereof, at least for now. We need to do more
work in the higher layers to properly deal with this, since we may
not get "normal" firmware notifications that are fragmented, only
RX, and then we need to put it back together and add the necessary
API to report a chain of things to the higher layers, this doesn't
fit into the struct iwl_rx_cmd_buffer today.

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.20200425130140.e78a59f70b1d.Ica656a98a4e4220d73edc97600edd680cbc97241@changeid