tests: Add a test-pseudotcp-fuzzy test for fuzzing PseudoTcpSocket

As documented at the top of the file, this creates two PseudoTcpSockets
in a loopback configuration, and mutates the raw packets which are sent
between them, hoping to cause assertion failures and illegal memory
accesses in the pseudotcp code.

Best run under Valgrind or GDB.
pseudotcp: Fix an assertion on an invalid calculated RTT

If a packet has an invalid tsecr field, invalid (e.g. negative) RTTs may
be calculated from it. If so, discard the packet as invalid.
pseudotcp: Fix partial acknowledgement of segments

If an incoming ACK acknowledges part of a pending SSegment, correctly
increment the base offset of that SSegment before attempting to transmit
it. Otherwise, the wrong data will be transmitted and the offset passed
to packet() will be incorrect.
add nice_component_state_to_string()

Nice to make debug logs more friendly to read.
Return the correct originating IP on TURN

If doing a recv on UDP-TURN, the 'from' address was kept set to
the turn server which causes connchecks to fail with "mismatched address"
error. This fixes it
Protect test-dribble against read->connected->ready state changes
Add more debug info when adding relays
component: socket has been renamed nicesock
component: Remove return value from *_restart() functions, they can't fail
conncheck: Factor out stopping connectivity checks
conncheck: Remove useless return value on conn_check_prune_stream
conncheck: Only stop conncheck timer if no stream has pending conn checks
conncheck: Make conn_check_free_item() static

It is never used outside of this file.
conncheck: Use g_slist_free_full() for conncheck list

Skips one iterator over g_slist_foreach() + g_slist_free(). It is also easier
to read.
stream: Clear connchecks on restart inside stream
agent: Add nice_agent_restart_stream() to restart a single stream
conncheck: Don't fail a stream that has on-going discovery
conncheck: Only print debug message if actually freeing something
stream: No need to pass RNG to stream_restart()

It can now take it from the agent.
factor out: component_clean_turn_servers()