packetdrill: fix 'error: SIOCGSTAMP undeclared'

Errors in some distributions looked like:

cc -g -Wall -Werror   -c -o packet_socket_linux.o packet_socket_linux.c
packet_socket_linux.c: In function `packet_socket_setup':
packet_socket_linux.c:100:26: error: `SIOCGSTAMP' undeclared (first use in this function)
  ioctl(psock->packet_fd, SIOCGSTAMP, &tv);
                          ^
packet_socket_linux.c:100:26: note: each undeclared identifier is reported only once for each function it appears in
packet_socket_linux.c: In function `packet_socket_receive':
packet_socket_linux.c:270:30: error: `SIOCGSTAMP' undeclared (first use in this function)
  if (ioctl(psock->packet_fd, SIOCGSTAMP, &tv) < 0)
                              ^

Signed-off-by: Sergey Chang <sergeychang@gmail.com>

gtests/net/packetdrill/packet_socket_linux.c

@@ -36,6 +36,7 @@
 
 #include <netpacket/packet.h>
 #include <linux/filter.h>
+#include <linux/sockios.h>
 
 #include "assert.h"
 #include "ethernet.h"