UDP_DATAGRAMSIZE at compile time

[sonoro1234]

Hello,

In order to change UDP_DATAGRAMSIZE at compile time but without modifying sources, it would be useful to have instead of:

luasocket/src/udp.h

Line 20 in 58c7608

#define UDP_DATAGRAMSIZE 8192

#ifndef UDP_DATAGRAMSIZE 
#define UDP_DATAGRAMSIZE 8192
#endif