Fix #213: sockaddr_in is undefined when compiling on FreeBSD

Make sure that <netinet/in.h> is included as per POSIX spec.

src/server/kiwix-serve.cpp

@@ -79,6 +79,7 @@ extern "C" {
 #include <netdb.h>
 #include <stdint.h>
 #include <sys/socket.h>
+#include <netinet/in.h>
 #include <unistd.h>
 #endif