[sr-dev] compiler warnings in master's siptrace

CC (gcc) [M siptrace.so] siptrace.o siptrace.c: In function 'trace_onreply_out': siptrace.c:1227:6: warning: unused variable 'len' [-Wunused-variable] int len; ^~~ siptrace.c: In function 'siptrace_net_data_recv': siptrace.c:1477:1: warning: label 'error' defined but not used [-Wunused-label] error: ^~~~~ siptrace.c:1436:6: warning: unused variable 'olen' [-Wunused-variable] int olen; ^~~~ siptrace.c:1435:8: warning: unused variable 'cp' [-Wunused-variable] char *cp; ^~ siptrace.c: In function 'siptrace_net_data_send': siptrace.c:1491:6: warning: unused variable 'olen' [-Wunused-variable] int olen; ^~~~ siptrace.c:1490:8: warning: unused variable 'p0' [-Wunused-variable] char *p0; ^~ siptrace.c:1489:8: warning: unused variable 'cp' [-Wunused-variable] char *cp; ^~