remove unused allocated field for cdata ptr

Signed-off-by: Qingping Hou <qingping.hou@gmail.com>
rename ktap_cdata.u.st to ktap_cdata.u.rec

to keep it consistent with kp_cdata_new_record

Signed-off-by: Qingping Hou <qingping.hou@gmail.com>
support ffi.new on non-array type

Signed-off-by: Qingping Hou <qingping.hou@gmail.com>
update tests for non-array ffi.new

Signed-off-by: Qingping Hou <qingping.hou@gmail.com>