ARP reuestion logc needs to do the right thing if (1) the address is a broadcast or multicast address, and (2) if the IP address lies outside of the network.  Thanks to Manuel Stuehn

ARP: Add signal logic so that we do not have to wait so long with the network responses to ARP requests quickly

Move some internal networking function protoypes out of the public include/nuttx/net/arp.h into to the private net/arp/arp.h

If CONFIG_NET_ARP_SEND is enabled, then all ICMP, TCP, and UDP send operations will call arp_send() before attempting the real send operation.  arp_send() will check if the the IP address mapping is in the ARP table and, if not send ARP requests periodically until it is.  This eliminates losing the first outgoing message because there is not mapping in the ARP table.

arp_poll(): inished the implementation of logic to send ARP requests.  Complete, fully hooked into the networking logic, and ready for test (but still untested)

arp_send.c: Partial implementation of logic to send ARP requests to assure that an IP address mapping is present in the ARP table

PKT sockets: Change how the IFF_NOARP flag is handled.  This should be set only when data is moved into the buffer and cleared after tested by the ARP logic.  Setting it globally can cause packets to be sent with no valid MAC addresses

arp_format.c: Move the logic that formats an ARP packet into a separate file where it can be re-used.

Move arp_arpin() from arp_inout.c to its own file. Rename arp_inout.c to arpipin.c because that is all that is left in the file

ARP: Add missing configuration option to select dumping of ARP packet headers.  Move ARP dumping logic from arp_inout.c to its own file

sscanf(): NuttX libc tried to guess how many characters to parse, extracted them into a buffer, then ran strtol() on that buffer. That guess is often wrong. A better approach would be to call strtol() directly on the input data, using the endptr return value to determine how many characters to skip after parsing.  From Kosma Moczek

NSH link management now works!  The last fix was to the Ethernet drivers:  They cannot disable clocking to the Ethernet blok on ifdown.  Otherwise, we cannot communicate with the PHY

Change the way PHY interrupts work: disable automatically.  Then we have to re-subscribe each time after the interrupt fires