Suppress pointless display of oplevels in ?chaninfo.

src/hash.* (modeNode_sort): Create as a "natural" sort order.
src/proto-p10.c (modeNode_sort): Rename to modeNode_sort_p10.
src/opserv.c (cmd_chaninfo): Clone and sort the membership array.  Only
    display oplevels if at least one member has a non-default oplevel.