opal/util/ethtool: add missing headers

and get Open MPI build on OpenBSD 6.0

opal/util/ethtool.c

@@ -18,6 +18,12 @@
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
 #endif
+#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_SOCKET_H
+#include <sys/socket.h>
+#endif
 #ifdef HAVE_NET_IF_H
 #include <net/if.h>
 #endif