This patch restores/fixes some of the behavior present in pre-netlink ndp(8).
# Deleting a local address now correctly returns `EPERM` (instead of `ENOENT`)
# `ndp -c` no longer dumps the entire table while complaining about local addresses
# Return exit code when deleting entry (e.g. trying `ndp -d` on a local address is an error)
There is still an issue with `ndp -s` creating duplicate entries. That will be addressed
in a separate patch.
Sponsored by: Rubicon Communications, LLC ("Netgate")