udp: align udp_encap_t_ to 2 cachelines

Based on the comments in the struct, udp_encap_t_ is meant to span 2
cachelines. Due to the 64 bit alignment of dpo_id_t, the struct spanned
3 cachelines. This caused fetching ue_ip_proto to trigger an additional
cache miss. This patch rearranges the ordering of the struct fields
so that udp_encap_t_ only spans 2 cachelines as intended.

before:
(gdb) print (int)&((struct udp_encap_t_*)0)->cacheline1
$8 = 128

after:
(gdb) print (int)&((struct udp_encap_t_*)0)->cacheline1
$1 = 64

Type: fix
Signed-off-by: Vadym Martsynovskyy <vmartsyn@fb.com>
Change-Id: I066c08654d4a8ef3e2d3954e957d4c5d382b209f
(cherry picked from commit 42386fc974)

src/vnet/udp/udp_encap.h

@@ -67,16 +67,16 @@ typedef struct udp_encap_t_
     } __attribute__ ((packed)) ip6;
   } __attribute__ ((packed)) ue_hdrs;
 
-  /**
-   * Flags controlling fixup behaviour
-   */
-  udp_encap_fixup_flags_t ue_flags;
-
   /**
    * The DPO used to forward to the next node in the VLIB graph
    */
   dpo_id_t ue_dpo;
 
+  /**
+   * Flags controlling fixup behaviour
+   */
+  udp_encap_fixup_flags_t ue_flags;
+
   /**
    * the protocol of the IP header imposed
    */