lsfd: optimize -i/--inet option

lsfd: optimize -i/--inet option

The original code filters sockets in convert() stage.
This code adds weak-filtering in collect_processes() stage to improve
the performe.

Without this optimization:

    # time ./lsfd --json -i > /tmp/lsfd.txt
    0.43user 0.57system 0:01.02elapsed 99%CPU (0avgtext+0avgdata 52724maxresident)k
    0inputs+0outputs (0major+14263minor)pagefaults 0swaps

With this optimization:

    # time ./lsfd --json -i > /tmp/lsfd-i.txt
    0.08user 0.27system 0:00.36elapsed 98%CPU (0avgtext+0avgdata 7060maxresident)k
    0inputs+0outputs (0major+2831minor)pagefaults 0swaps

About three times faster.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>