[meshcop] fix doxygen in ChannelMaskTlv::SetChannelMask() (#3693)
[meshcop] fix doxygen in ChannelMaskTlv::SetChannelMask() (#3693)


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