[CIFS] Do not overwrite aops

cifs should not be overwriting an element of the aops structure, since the
structure is shared by all cifs inodes.  Instead define a separate aops
structure to suit each purpose.

I also took the liberty of replacing a hard-coded 4096 with PAGE_CACHE_SIZE

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>
Signed-off-by: Steven French <sfrench@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>