busybox: convert netmsg and lock applet to "new style" applet definition

The "new style" busybox applet approach moves all config and build
definitions related to an applet to its .c file. This makes the
patches easier to maintain, as they only add new files to the busybox
build directory, without modifying BusyBox files.

Signed-off-by: Magnus Kroken <mkroken@gmail.com>
Tested-by: Koen Vandeputte <koen.vandeputte@ncentric.com>