use %m printf specifier where appropriate

function                                             old     new   delta
out                                                   85      75     -10
udhcpd_main                                         1472    1461     -11
open_stdio_to_tty                                     98      85     -13
init_exec                                            245     232     -13
udhcpc_main                                         2763    2749     -14
do_cmd                                              4771    4755     -16
status_line_bold_errno                                32      14     -18
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/7 up/down: 0/-95)             Total: -95 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 4548d4a..0013f4a 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -1631,7 +1631,7 @@
 				len = udhcp_recv_raw_packet(&packet, sockfd);
 			if (len == -1) {
 				/* Error is severe, reopen socket */
-				bb_error_msg("read error: %s, reopening socket", strerror(errno));
+				bb_error_msg("read error: "STRERROR_FMT", reopening socket" STRERROR_ERRNO);
 				sleep(discover_timeout); /* 3 seconds by default */
 				change_listen_mode(listen_mode); /* just close and reopen */
 			}