ipsec: move the IPSec SA pool out of ipsec_main

Type: refactor

this allows the ipsec_sa_get funtion to be moved from ipsec.h to
ipsec_sa.h where it belongs.
Also use ipsec_sa_get throughout the code base.

Signed-off-by: Neale Ranns <neale@graphiant.com>
Change-Id: I2dce726c4f7052b5507dd8dcfead0ed5604357df
diff --git a/src/vnet/ipsec/ah_encrypt.c b/src/vnet/ipsec/ah_encrypt.c
index a1f233c..c962ea9 100644
--- a/src/vnet/ipsec/ah_encrypt.c
+++ b/src/vnet/ipsec/ah_encrypt.c
@@ -176,7 +176,7 @@
 					     current_sa_pkts,
 					     current_sa_bytes);
 	  current_sa_index = vnet_buffer (b[0])->ipsec.sad_index;
-	  sa0 = pool_elt_at_index (im->sad, current_sa_index);
+	  sa0 = ipsec_sa_get (current_sa_index);
 
 	  current_sa_bytes = current_sa_pkts = 0;
 	}
@@ -387,7 +387,7 @@
     next:
       if (PREDICT_FALSE (b[0]->flags & VLIB_BUFFER_IS_TRACED))
 	{
-	  sa0 = vec_elt_at_index (im->sad, pd->sa_index);
+	  sa0 = ipsec_sa_get (pd->sa_index);
 	  ah_encrypt_trace_t *tr =
 	    vlib_add_trace (vm, node, b[0], sizeof (*tr));
 	  tr->spi = sa0->spi;