Immigration does not fall under the domestic policy. A domestic policy differs from foreign policy, which refers to the ways a government advances its interests in world politics.
These are the circumstances under which the protest of the students in Tinker v. Des Moines would be deemed unprotected speech:
if their action had clearly threatened order and safety.
And since it didn't, there was no reason for it to be deemed unprotected speech.
D. Trade can keep countries from specializing in producing certain goods.