netstat: fix IPv6 problem (garbage in scope_id); code shrink

netstat: fix IPv6 problem (garbage in scope_id); code shrink

function                                             old     new   delta
add_to_prg_cache_if_socket                             -     253    +253
print_inet_line                                      226     241     +15
udp_do_one                                           119     131     +12
tcp_do_one                                            65      77     +12
unix_do_one                                          530     529      -1
dir_act                                              215     207      -8
netstat_main                                         585     553     -32
.rodata                                           145592  145525     -67
file_act                                             255       -    -255
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 3/4 up/down: 292/-363)          Total: -71 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>