Changes

enb_proxy: add missing mme_info() to proxy_info()

As a bonus, `tried_mmes` now only serves its actual purpose - tracking
which MMEs have already been tried for selection filtering - rather
than being abused as a way to retrieve the current MME name.

Change-Id: Ibbb293d9e68b7c3a8c3ca7ee73132dbda3f2bf97
Related: SYS#7066