apps/nshlib:  Add the ping6 command to support checking IPv6 networks.  NSH logic is complete but still missing some network level support

Armv7-M: Remove Px4-only setting of stack to 0xff.  This is incompatible with standard NuttX stack montitoring logic

Armv7-M: Remove Px4-only setting of stack to 0xff.  This is incompatible with standard NuttX stack montitoring logic

Networking:  New domain field in socket structure is created by socket(), but missed cases where a socket is created via accept() or dup()

Networking:  Correct the value returned by accept() in the case where net_lockingwait() is called.  It was returning -1 and losing the errno value.  Noted by Rony Xln

Networking IPv6:  Fix and error when adding a neighbor to the table.  Comparing wrong address.  Add more debug info too

Networking:  IPv6 receipt logic errors.  Don't save neighbor address in table when solicitation is recieved.  Save it when the advertisement is received

All Ethernet drivers (again):  Missed one place where arp_out() is called and neighber_out() needs to be called

ICMPv6 Neighbor Advertisement:  Need to set O flag or response is not used.  Also, TTL=255 seems to be more-or-less standard in this message

Correct name of fields in struct sockaddr_in6:  sin6_port and sin6_family, not sin_port and sin_family

Networking:  When sending ICMPv6 advertisements and solicitations, set the NOARP bit so that we don't overwrite the destination MAC address