MINOR: connection: make sockaddr_alloc() take the address to be copied

Roughly half of the calls to sockadr_alloc() are made to copy an already
known address. Let's optionally pass it in argument so that the function
can handle the copy at the same time, this slightly simplifies its usage.
diff --git a/src/session.c b/src/session.c
index da271cf..f6e4fe4 100644
--- a/src/session.c
+++ b/src/session.c
@@ -147,11 +147,10 @@
 	if (unlikely((cli_conn = conn_new(&l->obj_type)) == NULL))
 		goto out_close;
 
-	if (!sockaddr_alloc(&cli_conn->src))
+	if (!sockaddr_alloc(&cli_conn->src, addr, sizeof(*addr)))
 		goto out_free_conn;
 
 	cli_conn->handle.fd = cfd;
-	*cli_conn->src = *addr;
 	cli_conn->flags |= CO_FL_ADDR_FROM_SET;
 	cli_conn->proxy_netns = l->rx.settings->netns;