busybox: update to 1.31.0

* Update busybox to version 1.31.0.
    New applets: ts, i2ctransfer
    New (restored) feature: error/info levels in syslog messages.
    Leave new features disabled by default.
* Refresh patches
* Remove patch that was backported from upstream

Config refreshed with commands below, after which the OpenWrt specific
config defaults (ipv6, login session child) were corrected:

  make package/busybox/compile   (to populate the build_dir)

  cd package/utils/busybox/config/
  ../convert_menuconfig.pl ../../../../build_dir/target-mips_24kc_musl/busybox-1.31.0

  cd package/utils/busybox
  ./convert_defaults.pl < ../../../build_dir/target-mips_24kc_musl/busybox-1.31.0/.config > Config-defaults.in

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

package/utils/busybox/patches/201-udhcpc_changed_ifindex.patch

@@ -1,6 +1,6 @@
 --- a/networking/udhcp/dhcpc.c
 +++ b/networking/udhcp/dhcpc.c
-@@ -1417,6 +1417,12 @@ int udhcpc_main(int argc UNUSED_PARAM, c
+@@ -1416,6 +1416,12 @@ int udhcpc_main(int argc UNUSED_PARAM, c
  		/* silence "uninitialized!" warning */
  		unsigned timestamp_before_wait = timestamp_before_wait;
  
@@ -8,8 +8,8 @@
 +		 * member interfaces were added/removed or if the status of the
 +		 * bridge changed).
 +		 * Workaround: refresh it here before processing the next packet */
-+		udhcp_read_interface(client_config.interface, &client_config.ifindex, NULL, client_config.client_mac);
++		udhcp_read_interface(client_data.interface, &client_data.ifindex, NULL, client_data.client_mac);
 +
- 		//bb_error_msg("sockfd:%d, listen_mode:%d", sockfd, listen_mode);
+ 		//bb_error_msg("sockfd:%d, listen_mode:%d", client_data.sockfd, client_data.listen_mode);
  
  		/* Was opening raw or udp socket here