ipsec: one thread index per-SA

Type: improvement

AN SA is uni-drectional therefore it can be used only for encrypt or
decrypt, not both. So it only needs one thread ID. free up some space on
the 1st cacheline.

Signed-off-by: Neale Ranns <neale@graphiant.com>
Change-Id: I21cb7cff70a763cbe2bffead860b574bc80b3136
diff --git a/src/vnet/ipsec/ipsec_sa.h b/src/vnet/ipsec/ipsec_sa.h
index 6ed7132..28ac931 100644
--- a/src/vnet/ipsec/ipsec_sa.h
+++ b/src/vnet/ipsec/ipsec_sa.h
@@ -116,8 +116,8 @@
   u8 crypto_iv_size;
   u8 esp_block_align;
   u8 integ_icv_size;
-  u32 encrypt_thread_index;
-  u32 decrypt_thread_index;
+  u32 thread_index;
+  u32 __pad_u32;
   u32 spi;
   u32 seq;
   u32 seq_hi;