selftests/net: msg_zerocopy enable build with older kernel headers

Explicitly define SO_EE_ORIGIN_ZEROCOPY.
This makes the test program build with older kernel headers,
e.g. from Debian 9.

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/net/msg_zerocopy.c

@@ -55,7 +55,7 @@
 #include <unistd.h>
 
 #ifndef SO_EE_ORIGIN_ZEROCOPY
-#define SO_EE_ORIGIN_ZEROCOPY		SO_EE_ORIGIN_UPAGE
+#define SO_EE_ORIGIN_ZEROCOPY		5
 #endif
 
 #ifndef SO_ZEROCOPY