[BUG] setup_network.sh: pnp address setting not working

[rleidner]

• openWB Version: 2026-07-21 11:00:06 +0200 [e4639bf]

main.log:
`got plug'n'play ip setting: '{"address": "192.168.193.251", "prefix": 24}'

got plug'n'play ip address: '192.168.193.251'

invalid plug'n'play ip address! assuming '192.168.193.250'

got plug'n'play ip prefix: '24'
`
Check for valid address is failing for correct IP address.