[linux-cifs-client] big performance improvement

[Steve French]

Big performance improvement - 

I changed to using mostly smaller buffers (well under 1 page) in the
cifs response processing - this cuts down more than 1/3
of the large allocations that cifs will do under heavy stress (lots of
processes going to the same server).  The order
3 memory allocation warnings running things like fsstress
with lots of processes were showing that Linux can badly 
fragment kernel memory and cause big performance problems
when applications allocate more than 2 pages at a time (cifs was
allocating 16.5K by default which results in an 8 page
allocation - which makes the kernel page manager work
hard under stress).

This should not hurt read responses or readdir (FindFirst) responses -
responses that need big buffers continue to get
them.

Over time I will fine tune the small cifs buffer size
(currently 256 bytes).