Add pcap file to exercise corner cases for BGP shutdown message printer

This pcap file contains 3 corner cases:
1. A packet with more data than the length provides for
2. A packet that has a shutdown message with zero data
3. A packet whose shutdown message length is longer than the remaining data
   in the notification

Author: fenner

tests/TESTLIST

@@ -60,6 +60,7 @@ bgp-llgr	bgp-evpn.pcap		bgp-llgr.out		-v
 bgp-encap	bgp-encap.pcap		bgp-encap.out		-v
 bgp-rt-prefix	bgp-rt-prefix.pcap	bgp-rt-prefix.out	-v
 bgp-extended-shutdown-msg	bgp-extended-shutdown-msg.pcapng	bgp-extended-shutdown-msg.out	-v
+bgp-shutdown-msg-variations	bgp-shutdown-msg-variations.pcap	bgp-shutdown-msg-variations.out	-v
 bgp-link-bw-extcommunity	bgp-link-bw-extcommunity.pcapng	bgp-link-bw-extcommunity.out	-v
 bgp-extended-msg	bgp-extended-msg.pcapng	bgp-extended-msg.out	-v
 bgp-enhanced-route-refresh	bgp-enhanced-route-refresh.pcapng	bgp-enhanced-route-refresh.out	-v

tests/bgp-shutdown-msg-variations.out

@@ -0,0 +1,11 @@
+    1  01:19:23.958779 IP (tos 0x0, ttl 64, id 1, offset 0, flags [none], proto TCP (6), length 81)
+    127.0.0.1.20 > 127.0.0.1.179: Flags [S], cksum 0xa709 (correct), seq 0:41, win 8192, length 41: BGP
+	Notification Message (3), length: 41, Cease (6), subcode Administrative Reset (4), Shutdown Communication (length: 10): "0123456789", Data: (length: 9)
+		0x0000:  4578 7472 6144 6174 61
+    2  01:19:23.960010 IP (tos 0x0, ttl 64, id 1, offset 0, flags [none], proto TCP (6), length 62)
+    127.0.0.1.20 > 127.0.0.1.179: Flags [S], cksum 0x89e7 (correct), seq 0:22, win 8192, length 22: BGP
+	Notification Message (3), length: 22, Cease (6), subcode Administrative Reset (4), empty Shutdown Communication
+    3  01:19:23.960948 IP (tos 0x0, ttl 64, id 1, offset 0, flags [none], proto TCP (6), length 72)
+    127.0.0.1.20 > 127.0.0.1.179: Flags [S], cksum 0x8489 (correct), seq 0:32, win 8192, length 32: BGP
+	Notification Message (3), length: 32, Cease (6), subcode Administrative Reset (4), invalid Shutdown Communication length, Data: (length: 11)
+		0x0000:  4030 3132 3334 3536 3738 39