sparse: Add guards to prevent FreeBSD-incompatible #include order.

FreeBSD insists that <sys/types.h> be included before <netinet/in.h> and
that <netinet/in.h> be included before <arpa/inet.h>.  This adds guards to
the "sparse" headers to yield a warning if this order is violated.  This
commit also adjusts the order of many #includes to suit this requirement.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Justin Pettit <jpettit@ovn.org>

lib/learning-switch.c

@@ -19,6 +19,7 @@
 
 #include <errno.h>
 #include <inttypes.h>
+#include <sys/types.h>
 #include <netinet/in.h>
 #include <stdlib.h>
 #include <time.h>