MINOR: server: generalize the "updater" source

the function server_parse_addr_change_request() contain an hardcoded
updater source "stats command". this function can be called from other
sources than the "stats command", so this patch make this argument
generic.
diff --git a/src/dumpstats.c b/src/dumpstats.c
index 8b55fe3..0ffbd5a 100644
--- a/src/dumpstats.c
+++ b/src/dumpstats.c
@@ -1600,7 +1600,7 @@
 				}
 			}
 			else if (strcmp(args[3], "addr") == 0) {
-				warning = server_parse_addr_change_request(sv, args[4]);
+				warning = server_parse_addr_change_request(sv, args[4], "stats command");
 				if (warning) {
 					appctx->ctx.cli.msg = warning;
 					appctx->st0 = STAT_CLI_PRINT;