dccp: Auto-load (when supported) CCID plugins for negotiation

dccp: Auto-load (when supported) CCID plugins for negotiation

This adds auto-loading of CCIDs (when module loading is enabled)
for the purpose of feature negotiation.

The problem with loading the CCIDs at the end of feature negotiation is
that this would happen in software interrupt context. Besides, if the host
advertises CCIDs during negotiation, it should have them ready to use, in
case an agreeing peer wants to use it for the connection.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>