libiproute: eliminate unused fields in struct filter_t's; style fixes

function                                             old     new   delta
print_route                                         1603    1588     -15
iproute_list_or_flush                               1254    1230     -24
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(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-39)             Total: -39 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2 files changed