Add bitswap tracer

[synzhu]

Add tracing for bitswap message sent / received.

[franklywatson]

Shouldn't there be tests with this?

[synzhu]

bors merge

[bors[bot]]

Build succeeded:

• Integration Tests (make -C integration access-tests)
• Integration Tests (make -C integration bft-tests)
• Integration Tests (make -C integration collection-tests)
• Integration Tests (make -C integration consensus-tests)
• Integration Tests (make -C integration epochs-tests)
• Integration Tests (make -C integration execution-tests)
• Integration Tests (make -C integration ghost-tests)
• Integration Tests (make -C integration mvp-tests)
• Integration Tests (make -C integration network-tests)
• Integration Tests (make -C integration verification-tests)
• Lint (./)
• Lint (./crypto/)
• Lint (./integration/)
• Unit Tests (access)
• Unit Tests (admin)
• Unit Tests (cmd)
• Unit Tests (consensus)
• Unit Tests (engine)
• Unit Tests (fvm)
• Unit Tests (ledger)
• Unit Tests (module)
• Unit Tests (network)
• Unit Tests (others)
• Unit Tests (utils)