ovs-thread: Avoid huge alignment on a base spinlock structure.

Marking the structure as 64 bytes aligned forces compiler to produce
big holes in the containing structures in order to fulfill this
requirement.  Also, any structure that contains this one as a member
automatically inherits this huge alignment making resulted memory
layout not efficient.  For example, 'struct umem_pool' currently
uses 3 full cache lines (192 bytes) with only 32 bytes of actual data:

  struct umem_pool {
    int                        index;                /*  0   4 */
    unsigned int               size;                 /*  4   4 */

    /* XXX 56 bytes hole, try to pack */

    /* --- cacheline 1 boundary (64 bytes) --- */
    struct ovs_spin lock __attribute__((__aligned__(64))); /* 64  64 */

    /* XXX last struct has 48 bytes of padding */

    /* --- cacheline 2 boundary (128 bytes) --- */
    void * *                   array;                /* 128  8 */

    /* size: 192, cachelines: 3, members: 4 */
    /* sum members: 80, holes: 1, sum holes: 56 */
    /* padding: 56 */
    /* paddings: 1, sum paddings: 48 */
    /* forced alignments: 1, forced holes: 1, sum forced holes: 56 */
  } __attribute__((__aligned__(64)));

Actual alignment of a spin lock is required only for Tx queue locks
inside netdev-afxdp to avoid false sharing, in all other cases
alignment only produces inefficient memory usage.

Also, CACHE_LINE_SIZE macro should be used instead of 64 as different
platforms may have different cache line sizes.

Using PADDED_MEMBERS to avoid alignment inheritance.

Fixes: ae36d63d7e ("ovs-thread: Make struct spin lock cache aligned.")
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: William Tu <u9012063@gmail.com>

lib/netdev-linux-private.h

@@ -108,7 +108,7 @@ struct netdev_linux {
     bool use_need_wakeup;
     bool requested_need_wakeup;
 
-    struct ovs_spin *tx_locks;  /* spin lock array for TX queues. */
+    struct netdev_afxdp_tx_lock *tx_locks;  /* Array of locks for TX queues. */
 #endif
 };