The previous refactoring of ucidef_set_interface() removed the protocol
selection heuristic which breaks the networking defaults for the majority
of boards.
Re-add the protocol selection and rename two bad "proto" references to
the expected "protocol" value.
Fixes: 85048a9c1f ("base-files: rework _ucidef_set_interface to be more generic")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>