There are two problems with libpcap headers: 1) why did you move them to /usr/include/pcap? Many sources I compile must be manually patched because they expect them to be under /usr/include. 2) pcap/pcap.h includes net/bpf.h, which is actually now pcap/net/bpf.h, so including pcap.h This problem is _very_ old. :-)
because libpcap contains by default: pcap.h pcap-namedb.h net/bpf.h and net contains basically system-level stuff, I think the intent was to clearly separate libpcap stuff from the rest. It's IMO ok solution for this. Patching can be minimized if 1) apps use autoconf :-), or 2) just add -I/usr/include/pcap in CFLAGS ;-) patching .h or .c files would be a real mess.. I tried that before starting to use -I/usr/include/pcap.