Change requested by Mark Lewis: accept area manager (areafix) netmail

requests sent to "SBBSecho" again. SBBSecho used to allow this back in
v3.02 (Nov-2017) and earlier versions, but was removed for loop-safety
since AreaMgr notifications and responses are sent from "SBBSecho", but
we have bot-loop protection built in, so that should be okay.