LU-5322 socklnd: handle sk_ready_data change in 3.15+ kernels

LU-5322 socklnd: handle sk_ready_data change in 3.15+ kernels

Starting with 3.15 kernels the sk_ready_data method in struct
sock only takes a single argument instead of two in earlier
kernels. Support this change in newer kernels.

Change-Id: Ifb740a931f454e806c74065c79ff912ed97e4e10
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Reviewed-on: http://review.whamcloud.com/11059
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>