apps/examples/bridge:  Lots of fixes.  I think it is working although I have still have host firewall issues in testing

Due to limitations in port unique-ness, have to use unique port numbers in apps/examples/bridge for now

apps/examples/bridge:  Add a simple UDP relay bridge for testing configurations with multiple networks

NSH USB Console:  Add logic to restart the console wait if an error occurs while reading from the console.  In USB console startup, the logic must be able to open the USB serial and receive 3 newlines.  However, it the USB driver is disconnected or otherwise fails before the 3 newlines are received, the receive loop becomes a killer, infinite loop, CPU hog.  Noted by spasbyspas

Network:  All logic will now handle varialbe length link layer protocol headers within incoming packets.  This permits use of multiple network interfaces with differing data links.  For example, ETHERNET + SLIP