SERVER-11776 Replication 'isself' check should allow mapped ports

'isself' should match the ports only if the hosts are being string matched. In cases where an instance is being addressed through a proxy port, port matching is an incorrect check - it invalidates a genuine match.

e.g. a mongod instance listening on port 27017 may be get redirected traffic from another port through IPtables routing. Such instances would fail to get added to a replica set for no good reason. Port proxies maybe required in multi-tenant cloud based systems where bind-able IPs/ports are NAT'ed.