lwip: removed unused return values of tcp_listen_input & tcp_timewait_input; fixed unused variable warning
lwip: removed unused return values of tcp_listen_input & tcp_timewait_input; fixed unused variable warning

Upstream commit: 5b0a47ca87724a527bc569ec9663aebc81d67ced

ambrop72/aprinter,johnkingsley/aprinter,ambrop72/aprinter,johnkingsley/aprinter,ambrop72/aprinter,johnkingsley/aprinter,ambrop72/aprinter,ambrop72/aprinter,johnkingsley/aprinter,ambrop72/aprinter,johnkingsley/aprinter,johnkingsley/aprinter,ambrop72/aprinter,johnkingsley/aprinter