test: add tests for datacarrier and datacarriersize options

Co-authored-by: Sebastian Falbesoner <sebastian.falbesoner@gmail.com>

test/functional/test_framework/messages.py

@@ -68,6 +68,9 @@ WITNESS_SCALE_FACTOR = 4
 DEFAULT_ANCESTOR_LIMIT = 25    # default max number of in-mempool ancestors
 DEFAULT_DESCENDANT_LIMIT = 25  # default max number of in-mempool descendants
 
+# Default setting for -datacarriersize. 80 bytes of data, +1 for OP_RETURN, +2 for the pushdata opcodes.
+MAX_OP_RETURN_RELAY = 83
+
 
 def sha256(s):
     return hashlib.sha256(s).digest()