server: request new peer after disconnection of non-persistent peers
server: request new peer after disconnection of non-persistent peers

Doing so ensures we reach our target number of outbound peers as soon as
possible. This is only necessary after calls to connmgr.Remove, as these
won't request a new peer connection.

btcsuite/btcd,tb00/btcd,btcsuite/btcd,ltcsuite/ltcd,tb00/btcd,ltcsuite/ltcd,davecgh/btcd,dajohi/btcd,dajohi/btcd,dajohi/btcd,davecgh/btcd