agent: Accept duplicated ports if no other option

agent: Accept duplicated ports if no other option

Commit a04fa4d492 introduced a new feature to try to have a different port for every
local candidate, even if they are on different interfaces. This breaks setups where the
application really wants a specific port and sets a range of exactly 1 port or a very small range.
In that case, if we can't find non-duplicated ports, then we just go around again and skip that check,
but only if both ports are in the same stream and component. Otherwise, we fail the whole component!