ss: Drop list traversal from unix_stats_print()

ss: Drop list traversal from unix_stats_print()

Although this complicates the dedicated procfs-based code path in
unix_show() a bit, it's the only sane way to get rid of unix_show_sock()
output diverging from other socket types in that it prints all socket
details in a new line.

As a side effect, it allows to eliminate all procfs specific code in
the same function.

Signed-off-by: Phil Sutter <phil@nwl.cc>