Improve LLS/LACP error messages

LACP can take a long time (seconds) to properly negotiate and configure, and in the meantime there can be LLS transmission errors that are logged. We should ignore these error messages while still configuring, and also warn the user if LACP is taking an unusually long time to configure since a failure might have occurred. For example, the link partner may not have LACP configured.

This feature should remove the relevant `TODO` in `lls/main.c`.