dump: collect_mappings -- Fix message text

@vma_area_list::longest is in pages not bytes.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
unix: Don't drop whole socket with unlinked path

When we can't stat socket name with ENOENT errno this
means, that the socket is bound and unlinked. Don't
drop the whole socket info, just treat it as nameless.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>