nat: Rename "struct sccp_connections" to "struct nat_sccp_connection"

The name sccp_connection is used in the osmo-sccp code, sccp_connections
was used in the NAT for tracking a sccp_connection. Rename it so it is
obvious that the struct belongs to the nat.

The rename was done with sed:
$ sed -i s,"struct sccp_connections","struct nat_sccp_connection",g \
		include/openbsc/*.h src/osmo-bsc_nat/* tests/*/*
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
index 2e6d9a3..b4c87d0 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
@@ -271,7 +271,7 @@
 	return 0;
 }
 
-void sccp_connection_destroy(struct sccp_connections *conn)
+void sccp_connection_destroy(struct nat_sccp_connection *conn)
 {
 	LOGP(DNAT, LOGL_DEBUG, "Destroy 0x%x <-> 0x%x mapping for con %p\n",
 	     sccp_src_ref_to_int(&conn->real_ref),
@@ -486,7 +486,7 @@
 	[NAT_CON_TYPE_OTHER]		= BCFG_CTR_CON_OTHER,
 };
 
-int bsc_conn_type_to_ctr(struct sccp_connections *conn)
+int bsc_conn_type_to_ctr(struct nat_sccp_connection *conn)
 {
 	return con_to_ctr[conn->con_type];
 }