Improve GPRS logging

* log xid type as string instead of int
* log packet encryption status, algorithm and IOV-UI in debug mode
* print encryption parameters when dumping llme via vty
* log key propagation from MM to LLC

Related: OS#1794
Change-Id: I30c38fdeb0b88bb39bdb9928851300bc79e6aec6
diff --git a/openbsc/src/gprs/gprs_sgsn.c b/openbsc/src/gprs/gprs_sgsn.c
index e5a54d9..e85e1a9 100644
--- a/openbsc/src/gprs/gprs_sgsn.c
+++ b/openbsc/src/gprs/gprs_sgsn.c
@@ -225,6 +225,8 @@
 	ctx->mm_state = GMM_DEREGISTERED;
 	ctx->auth_triplet.key_seq = GSM_KEY_SEQ_INVAL;
 	ctx->ciph_algo = sgsn->cfg.cipher;
+	LOGMMCTXP(LOGL_DEBUG, ctx, "Allocated with %s cipher.\n",
+		  get_value_string(gprs_cipher_names, ctx->ciph_algo));
 	ctx->ctrg = rate_ctr_group_alloc(ctx, &mmctx_ctrg_desc, tlli);
 	INIT_LLIST_HEAD(&ctx->pdp_list);