on a mount request, search a list of existing mounts for a given netroot
based on LUID entries (login ids). if an entry is found, then check the
current request rpcsec flavor against existing sessions/mounts. If no
match found, do another upcall for a mount and store a session of this
flavor for this LUID. if no entry found for this LUID, then do a mount
upcall, create a new entry and add it to the list.
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