The blockade would have been legal to prevent weapons getting into Gaza, but that wasn't the only purpose. The purpose of only allowing in a tinty number of goods was to punish the people of Gaza, to 'put them on a diet' as one one Israeli minister helpfully explained. That is illegal. Bibi's government also pretty much admitted the blockade wasn't a purely military matter when after the Mavi Marmara it almost instantly relaxed the blockade massively. If it was a legal and essential blockade, do you think it would have done that?
Two mortar shells explode in Golan Heights, no casualties or damage reported (Haaretz)