swconfig: fix portmap memory leak and hardening

swconfig: fix portmap memory leak and hardening

Free the per-port segment strings on unregister to avoid leaking them
across device rebind. Drop the dead (phys < 0) check and guard the
kstrdup allocation against failure.

Move swconfig_create_led_trigger() before list_add_tail() in
register_switch so a failing registration never publishes the device on
the global swdevs list with dangling portmap/portbuf pointers (a
use-after-free for any swdevs iterator). Route both the LED trigger
failure and the -ENFILE (swdev id exhaustion) failure paths through a
shared cleanup that frees portbuf, portmap, and the per-port segment
strings instead of leaking them.

Reorder the frees in unregister_switch to run after list_del so the
buffers are not freed while the device is still reachable from swdevs.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24246
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>