mptcp: Rename address-id for easier grepping

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
mptcp: Move setting of the bitfield to the fullmesh path-manager

This, to prepare full address-handling in the fullmesh path-manager.

Also, that way we reduce the need to have mptcp_loc4 in
mptcp_init4_subsockets.

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
mptcp: Refactor mptcp_find_addresses

This, to allow reusing it later in a more generic way.
We also had to change the address in the events to the union.

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
mptcp: Rename id to index and actually use it in fullmesh

To prepare the real support of 8 local addresses.

We need to create a second callback for the path-managers. One, that
gets the index and one that gets the address-id. This is ugly as hell,
but will be changed again very soon, when we move the whole
address-handling to the path-managers.

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
mptcp: Support 8 local addresses

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>