misc: ipaddr: fix return type of ipaddr_ipv4_mask_from_prefix()
misc: ipaddr: fix return type of ipaddr_ipv4_mask_from_prefix()

SeReRPRo/badvpn,SeReRPRo/badvpn,SeReRPRo/badvpn,SeReRPRo/badvpn,SeReRPRo/badvpn