TCP: skip_suspected_members=true prevents merge

When we have A and B and both have TCP.skip_suspected_members set to true, then the following happens on a network partition:

• A excludes B and adds B to suspected_members. Therefore A won't send any messages to B anymore
• B does the same
• A and B would remove the sender of a message from suspected_members, but nobody will actually send any messages !
• On a merge, A and B need to talk to each other, but both will discard the message !
  ==> A merge will never happen

WORKAROUND: set skip_suspected_members to false

SOLUTION: before a merge, clear suspected_members (maybe handle MERGE event)