: Finish up the feature negotiation during connection setup

This batch finishes the feature-negotiation during connection setup. The remaining batch considers exchanging FN options in established state, which is a different kettle of fish.

Patch #1: Introduces feature-activation handlers to dynamically
activate feature values after negotiation.

Patch #2: Integrates dynamic activation with socket initialisation (the full code
for pre-negotiation initialisation follows in patch #10).

Patch #3: Integrates dynamic activation with cild-socket creation.

Patch #4: Integrates dynamic activation at the client, before entering PARTOPEN.

Patch #5: Cleans up now unused bits of the infrastructure and updates copyrights.

Patch #6: Removes now unused bits of the CCID interface.

Patch #7: Removes test for LISTEN state in ccid3.c - CCIDs are now loaded only in
OPEN/PARTOPEN state.

Patch #8: Removes manual influence on NDP count feature - this is a CCID dependency.

Patch #9: Replaces the use of the boolean Ack Vector flag with an equivalent test
whether Ack Vectors are in use on the socket.

Patch #10: Initialisation framework for feature negotiation (pre-negotiation setup).

Patch #11: Auto-load CCIDs as part of the pre-negotiation setup. All advertised CCIDs
are pre-loaded, since feature negotiation is mostly in interrupt context. The modules are then ready to be used after the negotiation has converged.

Patch #12: Implement both sides of the Sequence Window feature (currently only one side
has been implemented).

Patch #13: Initialisation and type-checking of FN sysctl values.

Patch #14: Debugging and pretty-printing routines for feature negotiation.