DEBUG: ssl-sock/show_fd: Display SSL error code

Like for connection error code, when FD are dumps, the ssl error code is now
displayed. This may help to diagnose why a connection error occurred.

This patch may be backported to help debugging.
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index 97d2c3b..fc9de55 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -6998,7 +6998,7 @@
 		chunk_appendf(&trash, " xctx.conn=%p(BOGUS)", sctx->conn);
 		ret = 1;
 	}
-	chunk_appendf(&trash, " xctx.st=%d", sctx->xprt_st);
+	chunk_appendf(&trash, " xctx.st=%d .err=%ld", sctx->xprt_st, sctx->error_code);
 
 	if (sctx->xprt) {
 		chunk_appendf(&trash, " .xprt=%s", sctx->xprt->name);