port type could be changed even if port is linked

renderPortsForObject: render form controls even if port is linked
getExistingPortTypeOptions: check if port is linked and select only compatible types
mgmt link on FQDN supports any protocol

getMgmtProtosConfig: new func
formatAttributeValue: switch from hardcoded protocols array to the configured one
convertMgmtConfigVars: helper for converting old var values to the new format