Fixes maxParticipantAllowed user setting (fixes #247)

Like said in issue #247, the user setting maxParticipantAllowed when set before connecting is rewritten by RTCMultiConnection's function "setDirection".

In this fix, it remembers the value of maxParticipantAllowed if it is different from default value, executes setDirection's code, and recover user's value if set and if not one-to-one different of 1. (maybe not optimal way to do it)