include: get netinet/in.h before linux/tcp.h

... to allow build on older Linux dists (specifically CentOS 4.8 on gcc
4.8.5)

Closes #2160

lib/sendf.c

@@ -22,6 +22,10 @@
 
 #include "curl_setup.h"
 
+#ifdef HAVE_NETINET_IN_H
+#include <netinet/in.h>
+#endif
+
 #ifdef HAVE_LINUX_TCP_H
 #include <linux/tcp.h>
 #endif

lib/setopt.c

@@ -26,6 +26,10 @@
 #include <limits.h>
 #endif
 
+#ifdef HAVE_NETINET_IN_H
+#include <netinet/in.h>
+#endif
+
 #ifdef HAVE_LINUX_TCP_H
 #include <linux/tcp.h>
 #endif