Rename the suffix of a pcapng test file to .pcapng

[skip ci]

Author: fxlb

tests/TESTLIST

@@ -915,7 +915,7 @@ ios_nhrp			ios_nhrp.pcap			ios_nhrp.out	-v
 NHRP_registration		NHRP_registration.pcap		NHRP_registration.out	-v
 NHRP-responder-address		NHRP-responder-address.pcap	NHRP-responder-address.out	-v
 nhrp-trace			nhrp-trace.pcap			nhrp-trace.out	-v
-nhrp				nhrp.pcap			nhrp.out	-v
+nhrp				nhrp.pcapng			nhrp.out	-v
 pb_nhrp_1			pb_nhrp_1.pcap			pb_nhrp_1.out	-v
 
 # Undefined behavior tests