[iwm] Get rid of SYNC_RESP_STRUCT and SYNC_RESP_PTR macros.

[ivadasz]

Summary

SYNC_RESP_STRUCT and SYNC_RESP_PTR originate from the OpenBSD version of
iwm, and they weren't serving any real purpose in the FreeBSD port.

We just do a single bus_dmamap_sync for syncing the complete received frame,
instead of explicitly bus_dmamap_sync-ing subranges of the frame like in
the OpenBSD iwm code.

[adrian]

hm, so we're already correctly sync'ing the payload as well as the descriptor?

[ivadasz]

In (line numbers from right side of the diff) line 5034 the descriptors are synced, and in line 5049 the payload is synced. All the SYNC_RESP_STRUCT macro usages were just repeating the syncing of the payload.