Made ARP protocol more robust

Signed-off-by: J. German Rivera <German.Rivera@freescale.com>
Fixed self-deadlock when sending ping reply from packet receive thread

Sending an IP packet may block waiting for ARP resolution. If
the thread sending the IP packet is the packet receive thread,
and it gets blocked waiting for ARP resolution, this thread
will self-deadlock, as no further packets can be received,
including the ARP reply, it is waiting for.

Signed-off-by: J. German Rivera <German.Rivera@freescale.com>