iwlagn: move IO functions out of line

This generates a massive reduction in module size:
with debug:
   text	   data	    bss	    dec	    hex	filename
 670300	  13136	    420	 683856	  a6f50	iwlagn.ko (before)
 388347	  13136	    408	 401891	  621e3	iwlagn.ko (after)

without debug:
   text	   data	    bss	    dec	    hex	filename
 528575	  13072	    420	 542067	  84573	iwlagn.ko (before)
 294192	  13072	    408	 307672	  4b1d8	iwlagn.ko (after)

This also removes all the IO debug functionality since
it can easily be replaced by tracing, and makes the
code unnecessarily complex.

I haven't done any CPU utilisation measurements, but
given that the hotpaths don't use much IO it is not
likely to have a negative impact; in fact, the size
reduction will reduce cache pressure which possibly
improves performance.

Finally, an unused function or two were removed.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>