Don't include sys/socket.h

It's not available on all OSs, e_os.h already does the right thing
Reviewed-by: NRichard Levitte <levitte@openssl.org>

MR: #1870

test/dtlsv1listentest.c

@@ -56,7 +56,6 @@
  */
 
 #include <string.h>
-#include <sys/socket.h>
 #include <openssl/ssl.h>
 #include <openssl/bio.h>
 #include <openssl/err.h>