Tests: Refactor payload_to_info()

All callers of payload_to_info were required to wrap payload with str().
Refactor to call scapy's payload.load for raw payloads or specify the
specific fieldname.

Change-Id: I1c80599d4df8dc129dbb8274733afaad406d5bcf
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>

test/test_l2xc_multi_instance.py

@@ -235,7 +235,7 @@ class TestL2xcMultiInst(VppTestCase):
             last_info[i.sw_if_index] = None
         dst_sw_if_index = pg_if.sw_if_index
         for packet in capture:
-            payload_info = self.payload_to_info(str(packet[Raw]))
+            payload_info = self.payload_to_info(packet[Raw])
             try:
                 ip = packet[IP]
                 udp = packet[UDP]