If __rte_cache_aligned is not defined (rte_memory.h is not included),
the code compiles but the structure is not aligned... it defines the
structure and creates a global variable called __rte_cache_aligned.
And this can lead to really bad things if this code is in a .h that
is included by files that may or may not include rte_memory.h
Signed-off-by: Jia Yu <jyu@vmware.com> Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>