Andrew Zaborowski authored Oct 18, 2018 and Thomas Haller committed Oct 23, 2018

interface_added expects mirror_8021x_connection() to return the pointer to
the existing connection if one exists, and NULL on error, rather than
NULL if a conneciton exists.  While touching that, add logic to return
specifically a connection with EAP method set to 'external' if one
exists even though this should not affect any other logic we have
currently.