Loosen requirements for connecting to debugnet-type servers. Only require a
destination address; the rest can theoretically be inferred from the routing
table. (If the routing table is potentially damaged, one can always specify
the parameters explicitly with the same option flags as before.
Relax corresponding constraints in netdump(4) and move ifp validation to
debugnet connection time.
Submitted by: John Reimer <john.reimer AT emc.com> (earlier version)