Refresh all configurations that have Telnetd enabled; those configurations now also need the telnet driver

Top-level Makefiles: Check if CONFIG_ARCH_BOARD_CUSTOM_DIR_RELPATH is enabled

drivers/net/telnet.c:  Now works like the loop device.  A new interface called telnet_initialize() registers a telnet session "factory" device at /dev/telnet.  Via ioctl, the factory device can create instances of the telnet character devices at /dev/telnetN to support Telnet sessions.

USB serial driver Kconfig: Select default sizes for serial buffers so that the can hold even multiples of the max packet size.

Also added warnings:  There are some concurrency issues in the current implementation if you try to modify the procfs data structures will the procfs is mounted and possibly busy.

s/procfs:  The procfs file system can now be configured so that it supports a runtime registration of procfs entries with CONFIG_FS_PROCFS_REGISTER=y

Remove CONFIG_NET_PINGADDRCONF.  This was a uIP way of assigning IP addresses, but is not standard and not a appropriate feature in general.