Fix invalid read caused by wrong memcpy size.

Valgrind report:

Invalid read of size 8
   at 0x41CCB7: get_socket.constprop.1 (udp.c:81)
   by 0x41CDC7: udp_connect_input (udp.c:102)
   by 0x404BDE: main (tsdecrypt.c:978)
 Address 0x607a410 is 0 bytes after a block of size 64 alloc'd
   at 0x4C2A359: malloc (vg_replace_malloc.c:270)
   by 0x594955C: gaih_inet (in /lib64/libc-2.17.so)
   by 0x594D18C: getaddrinfo (in /lib64/libc-2.17.so)
   by 0x41CB95: get_socket.constprop.1 (udp.c:61)
   by 0x41CDC7: udp_connect_input (udp.c:102)
   by 0x404BDE: main (tsdecrypt.c:978)