[mle] allow setting router eligible attr to false for MTD (#4450)
[mle] allow setting router eligible attr to false for MTD (#4450)


jwhui/openthread,bukepo/openthread,bukepo/openthread,lanyuwen/openthread,bukepo/openthread,srickardti/openthread,lanyuwen/openthread,lanyuwen/openthread,jwhui/openthread,librasungirl/openthread,chshu/openthread,librasungirl/openthread,lanyuwen/openthread,jwhui/openthread,abtink/openthread,lanyuwen/openthread,abtink/openthread,srickardti/openthread,chshu/openthread,openthread/openthread,srickardti/openthread,openthread/openthread,bukepo/openthread,srickardti/openthread,abtink/openthread,jwhui/openthread,chshu/openthread,chshu/openthread,openthread/openthread,abtink/openthread,chshu/openthread,openthread/openthread,chshu/openthread,librasungirl/openthread,librasungirl/openthread,lanyuwen/openthread