MINOR: remove the client/server side distinction in SI addresses

Stream interfaces used to distinguish between client and server addresses
because they were previously of different types (sockaddr_storage for the
client, sockaddr_in for the server). This is not the case anymore, and this
distinction is confusing at best and has caused a number of regressions to
be introduced in the process of converting everything to full-ipv6. We can
now remove this and have a much cleaner code.
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index 27a2f97..4f0bfa2 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -178,16 +178,10 @@
 			} cli;
 		} ctx;					/* used by stats I/O handlers to dump the stats */
 	} applet;
-	union {
-		struct {
-			struct sockaddr_storage from;	/* the client address */
-			struct sockaddr_storage to;	/* the address reached by the client if SN_FRT_ADDR_SET is set */
-		} c; /* client side */
-		struct {
-			struct sockaddr_storage from;	/* the address to spoof when connecting to the server (transparent mode) */
-			struct sockaddr_storage to;	/* the address to connect to */
-		} s; /* server side */
-	} addr; /* addresses of the remote side */
+	struct {
+		struct sockaddr_storage from;	/* client address, or address to spoof when connecting to the server */
+		struct sockaddr_storage to;	/* address reached by the client if SN_FRT_ADDR_SET is set, or address to connect to */
+	} addr; /* addresses of the remote side, client for producer and server for consumer */
 };
 
 /* An applet designed to run in a stream interface */