Since https://github.com/weaveworks/tcptracer-bpf/pull/39, tcptracer-bpf
can generate "fd_install" events when a process installs a new file
descriptor in its fd table. Those events must be requested explicitely
on a per-pid basis with tracer.AddFdInstallWatcher(pid).
This is useful to know about "accept" events that would otherwise be
missed because kretprobes are not triggered for functions that were
called before the installation of the kretprobe.
This patch find all the processes that are currently blocked on an
accept() syscall during the EbpfTracker initialization.
feedInitialConnections() will use tracer.AddFdInstallWatcher() to
subscribe to fd_install events. When a fd_install event is received,
synthesise an accept event with the connection tuple and the network
namespace (from /proc).
This fixes the regression where process names weren't appearing for
Darwin probes. Makes testing easier.
Also, changes the process walker to operate on value types. There's no
performance advantage to using reference types for something of this
size, and there appeared to be a data race in the Darwin port that
caused nodes to gain and lose process names over time.
Also, restructures how to enable docker scraping. Default false when run
manually, and enabled via --probe.docker true in the scope script.
