This delegates the construction of the server Endpoint object to the i2p/tor
Provider, which can use the i2p/tor section of the config file to add options
which would be awkward to express as text in an endpoint descriptor string.
refs ticket:2889 (but note this merely makes room for a function to be
written that can process I2CP options, it does not actually handle such
options, so it does not close this ticket yet)
If no session management is performed, txi2p starts a process-wide session the
first time a connection (client or server) is opened; all subsequent connections
use that session and its configuration properties.
This commit ensures that the same properties are passed to both client and
server endpoints, so that the correct I2P Destination is started regardless of
whether the first connection made by Tahoe-LAFS is for a client or server.
Closes#2858.
