common/admin_socket: Copy fewer strings

common/admin_socket: Copy fewer strings

Pass std::string_view to call, rather than passing strings by value.

Change cmdmap_t and the maps in admin_socket to use the std::less<>
transparent comparator, so we can compare string_views to strings. (Or
anything else with an equality operator with strings.)

Pass the cmdmap_t in to call by const reference, not reference.

The change to cmdmap_t requires changing some of the users of
cmdmap_t. (That is, make them actually use cmdmap_t explicitly, not
the open-coed map type.)

Signed-off-by: Adam C. Emerson <aemerson@redhat.com>