libbb: new option FEATURE_ETC_SERVICES: if off, /etc/services reads often avoided

In practice, "wget http://host.com/" always uses port 80.
People explicitly set non-standard ports via options or parameters
("telnet 1.2.3.4 567" or "telnet 1.2.3.4 ftp") instead of modifying
/etc/services.

function                                             old     new   delta
telnet_main                                         1466    1464      -2
rdate_main                                           215     198     -17
fakeidentd_main                                      269     252     -17
parse_url                                            459     392     -67
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-103)           Total: -103 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/util-linux/rdate.c b/util-linux/rdate.c
index f27294e..5ec7952 100644
--- a/util-linux/rdate.c
+++ b/util-linux/rdate.c
@@ -45,7 +45,7 @@
 	alarm(10);
 	signal(SIGALRM, socket_timeout);
 
-	fd = create_and_connect_stream_or_die(host, bb_lookup_port("time", "tcp", 37));
+	fd = create_and_connect_stream_or_die(host, bb_lookup_std_port("time", "tcp", 37));
 
 	if (safe_read(fd, &nett, 4) != 4)    /* read time from server */
 		bb_error_msg_and_die("%s: %s", host, "short read");