[meshcop] process ChannelMaskTlv in message (#3690)
[meshcop] process ChannelMaskTlv in message (#3690)

Allows arbitrary number of Channel Mask entries.
abtink/openthread,abtink/openthread,lanyuwen/openthread,chshu/openthread,librasungirl/openthread,lanyuwen/openthread,chshu/openthread,bukepo/openthread,chshu/openthread,srickardti/openthread,abtink/openthread,srickardti/openthread,jwhui/openthread,openthread/openthread,chshu/openthread,librasungirl/openthread,openthread/openthread,abtink/openthread,bukepo/openthread,turon/openthread,jwhui/openthread,librasungirl/openthread,librasungirl/openthread,srickardti/openthread,jwhui/openthread,lanyuwen/openthread,openthread/openthread,chshu/openthread,srickardti/openthread,bukepo/openthread,jwhui/openthread,lanyuwen/openthread,lanyuwen/openthread,bukepo/openthread,lanyuwen/openthread,turon/openthread,chshu/openthread,turon/openthread,openthread/openthread,turon/openthread