dpaa2-switch: rework FDB management on the bridge leave path

In the Linux kernel, the following vulnerability has been resolved: dpaa2-switch: rework FDB management on the bridge leave path On bridge leave, the dpaa2_switch_port_set_fdb() function always allocates a new FDB for the port which is becoming standalone. In case no FDB is found, then the port leaving a bridge will continue to use the current one. The above logic does not cover the case in which there are multiple bridges which have ports from the same DPSW instance. In this case, when the last port leaves bridge #1, it finds an unused FDB to switch to, but the old FDB is not marked as unused. Since the number of FDBs is equal to the number of DPSW interfaces, this will eventually lead to multiple ports sharing the same FDB. Fix this by changing how we are managing the FDBs on the leave path. Instead of directly allocating a new FDB, first verify if the current port is the last one to leave a bridge. If this is the case, then continue to use the current FDB and only allocate another FDB if there are other ports remaining in the bridge.