nl_bridge: bridge_stp_states: use std::map::insert_or_assign
nl_bridge: bridge_stp_states: use std::map::insert_or_assign

Since we do not care if there was a previous value, we can use
std::map::insert_or_assign to set the stp state map values instead of
first checking if there was a previous value and erasing it.

Signed-off-by: Jonas Gorski <9712c064bde5a52658fc87d6454b4956f9bf286b@bisdn.de>

bisdn/basebox,bisdn/basebox,bisdn/basebox,bisdn/basebox