Fix compile errors on OpenBSD

- <pthread.h> included for the "pthread_t" type definition.
- <net/ethernet.h> include removed as the header doesn't exist.
- AI_ALL and AI_V4MAPPED defined to 0 as the options don't exist.

src/Cedar/BridgeUnix.c

@@ -25,11 +25,14 @@
 #include <errno.h>
 #include <fcntl.h>
 
-#include <net/ethernet.h>
 #include <net/if.h>
 #include <sys/ioctl.h>
 #include <sys/stat.h>
 
+#ifndef UNIX_OPENBSD
+#include <net/ethernet.h>
+#endif
+
 #ifdef UNIX_SOLARIS
 #include <sys/sockio.h>
 #endif