[mpl] fix bug in comparing sequence numbers (#3588)
[mpl] fix bug in comparing sequence numbers (#3588)

Fix serial number arithmetic due to value wrap.
jwhui/openthread,bukepo/openthread,abtink/openthread,openthread/openthread,lanyuwen/openthread,librasungirl/openthread,srickardti/openthread,turon/openthread,bukepo/openthread,abtink/openthread,chshu/openthread,abtink/openthread,turon/openthread,lanyuwen/openthread,turon/openthread,openthread/openthread,lanyuwen/openthread,chshu/openthread,lanyuwen/openthread,turon/openthread,lanyuwen/openthread,jwhui/openthread,bukepo/openthread,abtink/openthread,librasungirl/openthread,jwhui/openthread,chshu/openthread,srickardti/openthread,openthread/openthread,jwhui/openthread,librasungirl/openthread,srickardti/openthread,librasungirl/openthread,bukepo/openthread,chshu/openthread,chshu/openthread,srickardti/openthread,openthread/openthread,chshu/openthread,lanyuwen/openthread