cosmetic: comments, log typo, explicit pointer

Fix log typo 'REGSITER' and add some comments on UE Register with TMSI.

The container_pair struct starts with 'list', so passing the container_pair
pointer is equivalent to passing the list; but instead, explicitly mention the
list member to avoid confusion.
diff --git a/src/ranap_msg_factory.c b/src/ranap_msg_factory.c
index 6cf997d..7e03b13 100644
--- a/src/ranap_msg_factory.c
+++ b/src/ranap_msg_factory.c
@@ -814,7 +814,7 @@
 
 	RANAP_ProtocolIE_ContainerPair_t *container_pair = CALLOC(1, sizeof(*container_pair));
 	/* Add the pair to the list of IEs of the RAB ass.req */
-	ASN_SEQUENCE_ADD(container_pair, pair);
+	ASN_SEQUENCE_ADD(&container_pair->list, pair);
 	/* Add the pair to the list of IEs of the RAB ass.req */
 	ASN_SEQUENCE_ADD(&ies.raB_SetupOrModifyList.list, container_pair);