register multiple algortihms

[fcangialosi]

in the current model, a calling application creates an instance alg of some struct implementing CongAlg and then (indirectly) calls portus::run_inner(..., alg), and portus assumes all new connections from the datapath should use this alg.

this limits applications to using one ccp algorithm at a time.

rather than having a separate ccp process for each algorithm, it probably makes more sense for a single process to be able to handle connections using different algorithms.

i think the minimally invasive change to support this would be to:

• modify run_inner to instead take a list of CongAlgs rather than just a single one
• have libccp send the name of the algorithm it wants to use in the Create message (for backwards-compatibility we could also specify the index of a default alg so that even if libccp leaves the algorithm field blank as it currently does, portus can still do something reasonable)
• look up the appropriate CongAlg in the list and call new_flow on that