Add INTERWORKING_ADD_NETWORK command

Add INTERWORKING_ADD_NETWORK command

This can be used to provide more control to upper layers on network
blocks generated as part of Interworking network selection.
INTERWORKING_ADD_NETWORK behaves otherwise identically to
INTERWORKING_CONNECT, but it does not request a new connection after
having added the network block and it returns the network id of the
added network.

INTERWORKING_ADD_NETWORK followed by REASSOCIATE would behave more or
less identically to INTERWORKING_CONNECT, but this allows the created
network profile to be modified, if desired, and/or stored externally.
SELECT_NETWORK can also be used with the network id returned from
INTERWORKING_ADD_NETWORK to enforce that specific network profile to be
used for the next connection (though, it should be noted that this
behavior may not meet all Hotspot 2.0 requirements if there were other
enabled networks that could have higher priority).

Signed-off-by: Jouni Malinen <j@w1.fi>