pcap_lookupnet doesn't know about rpcap devices

[johnthacker]

• This is not a security issue (See first line).

pcap_lookupnet has special handling for a number of device names to just silently return 0, but doesn't have any handling for rpcap devices. This causes a spurious warning message with the tcpdump -f flag, and possibly could cause errors elsewhere:

$ ./build/tcpdump -d -i "rpcap://127.0.0.1/enp6s0" "vlan" -f
tcpdump: WARNING: foreign (-f) flag used but: SIOCGIFADDR: rpcap://127.0.0.1/enp6s0: No such device
(000) ldh      [12]
(001) jeq      #0x8100          jt 4	jf 2
(002) jeq      #0x88a8          jt 4	jf 3
(003) jeq      #0x9100          jt 4	jf 5
(004) ret      #262144
(005) ret      #0

A remote device that doesn't actually exist fails earlier as expected:

$ ./build/tcpdump -d -i "rpcap://127.0.0.1/nosuchdev" "vlan" -f
tcpdump: enp6s0sds: No such device exists (No such device exists)

(I suppose it could somehow query the device if possible, or succeed with a warning that the function isn't supported on remote devices, instead of silently returning 0.)

$ pcap-config --version
1.11.0-PRE-GIT