isLooped checks for any duplicate prefixes

[everett1992]

previous implemenation only checked for duplicates self_id. A node would happily forward a packet that had signs it was already looped. Since not all nodes in a network will enable loop detection I want configured nodes to drop these packets.

This is a quadratic loop, but it's upper bound is 64. It can be improved with a better data structure but I wanted to keep it simple.

The package doesn't have a test framework so I wrote a small harness to double check the behavior. All the 'self' tests pass with the previous impl.

runTest(1, {0x11, 0x22, 0x33}, max_loop_strict, false, "no dups");
runTest(1, {0xAA, 0x22}, max_loop_strict, true, "dup with self");
runTest(1, {0x11, 0x11, 0x22, 0x33}, max_loop_strict, true, "dup in path");
runTest(2, {0xAA, 0x22, 0xBB, 0x44}, max_loop_strict, false, "2-byte no dup");
runTest(2, {0xAA, 0xBB, 0xCC, 0xDD}, max_loop_strict, true, "2-byte dup with self");
runTest(2, {0x00, 0x11, 0x00, 0x11}, max_loop_strict, true, "2-byte dup in path");
runTest(3, {0xAA, 0xBB, 0xCC}, max_loop_strict, true, "3-byte dup with self");
runTest(3, {0x11, 0x22, 0x33, 0x11, 0x22, 0x33}, max_loop_strict, true, "3-byte dup in path");

runTest(1, {0x11, 0x11, 0x11, 0x11}, max_loop_minimal, false, "4 repeats: under minimal limit");
runTest(1, {0x11, 0x11, 0x11, 0x11, 0x11}, max_loop_minimal, true, "5 repeats: over minimal limit");
runTest(1, {0xAA, 0xAA, 0xAA}, max_loop_minimal, false, "3 repeats and self: under minimal limit");
runTest(1, {0xAA, 0xAA, 0xAA, 0xAA}, max_loop_minimal, true, "4 repeats and self: over minimal limit");