BUILD: peers: fix build warning with gcc 4.2.1

Building on OpenBSD 6.7 with gcc-4.2.1 yields the following warnings
which suggest that the initialization is not taken as expected but
that the container member is reset with each initialization:

  src/peers.c: In function 'peer_send_updatemsg':
  src/peers.c:1000: warning: initialized field overwritten
  src/peers.c:1000: warning: (near initialization for 'p.updt')
  src/peers.c:1001: warning: initialized field overwritten
  src/peers.c:1001: warning: (near initialization for 'p.updt')
  src/peers.c:1002: warning: initialized field overwritten
  src/peers.c:1002: warning: (near initialization for 'p.updt')
  src/peers.c:1003: warning: initialized field overwritten
  src/peers.c:1003: warning: (near initialization for 'p.updt')
  src/peers.c:1004: warning: initialized field overwritten
  src/peers.c:1004: warning: (near initialization for 'p.updt')

Fixing this is trivial, we just have to initialize one level at
a time.
diff --git a/src/peers.c b/src/peers.c
index f16ba8e..47582e4 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -995,12 +995,14 @@
                                       unsigned int updateid, int use_identifier, int use_timed)
 {
 	struct peer_prep_params p = {
-		.updt.stksess = ts,
-		.updt.shared_table = st,
-		.updt.updateid = updateid,
-		.updt.use_identifier = use_identifier,
-		.updt.use_timed = use_timed,
-		.updt.peer = appctx->ctx.peers.ptr,
+		.updt = {
+			.stksess = ts,
+			.shared_table = st,
+			.updateid = updateid,
+			.use_identifier = use_identifier,
+			.use_timed = use_timed,
+			.peer = appctx->ctx.peers.ptr,
+		},
 	};
 
 	return peer_send_msg(appctx, peer_prepare_updatemsg, &p);