Harmonize vec/pool_get_aligned object sizes and alignment requests

Object sizes must evenly divide alignment requests, or vice
versa. Otherwise, only the first object will be aligned as
requested.

Three choices: add CLIB_CACHE_LINE_ALIGN_MARK(align_me) at
the end of structures, manually pad to an even divisor or multiple of
the alignment request, or use plain vectors/pools.

static assert for enforcement.

Change-Id: I41aa6ff1a58267301d32aaf4b9cd24678ac1c147
Signed-off-by: Dave Barach <dbarach@cisco.com>
diff --git a/src/vnet/dpo/mpls_label_dpo.h b/src/vnet/dpo/mpls_label_dpo.h
index 98c88f7..4e032d3 100644
--- a/src/vnet/dpo/mpls_label_dpo.h
+++ b/src/vnet/dpo/mpls_label_dpo.h
@@ -67,6 +67,12 @@
 typedef struct mpls_label_dpo_t
 {
     /**
+     * required for pool_get_aligned.
+     *  memebers used in the switch path come first!
+     */
+    CLIB_CACHE_LINE_ALIGN_MARK(cacheline0);
+
+    /**
      * The MPLS label header to impose. Outer most label first.
      * Each DPO will occupy one cache line, stuff that many labels in.
      */