802.15.4 test Application:

 1) Loopback in single qemu:
 Enable CONFIG_NETWORKING_WITH_15_4_LOOPBACK config option in prj_x86/arm.conf
 to test 802.15.4. By enabling this option dummy driver will feed sending
 802.15.4 frames back to 15_4 Rx FIFO. 15_4 Rx FIFO will asseble all frames
 and feed it to IP Rx FIFO.

 2) Loopback between two qemus:
 Enable CONFIG_NETWORKING_WITH_15_4_LOOPBACK_UART config option in
 prj_x86/arm.conf to send 802.15.4 frames out through QEMU UART and receive
 frames through QEMU UART.

 Follow below simple steps to create fifos at host.

 $ mkfifo /tmp/ip-15-4-1.{in,out}
 $ ln /tmp/ip-15-4-1.in /tmp/ip-15-4-2.out
 $ ln /tmp/ip-15-4-1.out /tmp/ip-15-4-2.in

 Open two terminals and run two qemus with below options.
 $ make qemu QEMU_NUM=1 CONFIG_NETWORKING_WITH_15_4_LOOPBACK_UART=y
 $ make qemu QEMU_NUM=2 CONFIG_NETWORKING_WITH_15_4_LOOPBACK_UART=y