MINOR: server: Add a dictionary for server names.

This patch only declares and defines a dictionary for the server
names (stored as ->id member field).
diff --git a/include/types/server.h b/include/types/server.h
index 574d40e..4a07726 100644
--- a/include/types/server.h
+++ b/include/types/server.h
@@ -175,6 +175,9 @@
 #define SRV_SSL_O_EARLY_DATA   0x400  /* Allow using early data */
 #endif
 
+/* The server names dictionary */
+extern struct dict server_name_dict;
+
 struct pid_list {
 	struct list list;
 	pid_t pid;