libiproute: use stdout directly instead of passing it as a parameter

libiproute: use stdout directly instead of passing it as a parameter

function                                             old     new   delta
iprule_list                                           86      82      -4
print_rule                                           860     791     -69
ipaddr_list_or_flush                                2484    2384    -100
print_addrinfo                                      1498    1292    -206
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(add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-379)           Total: -379 bytes