cfm: Fix GCC warning.

cfm: Fix GCC warning.

On 32-bit platforms GCC warns:
../lib/cfm.c: In function 'compose_ccm':
../lib/cfm.c:130: warning: integer constant is too large for 'long' type
../lib/cfm.c: In function 'cfm_should_process_flow':
../lib/cfm.c:375: warning: integer constant is too large for 'long' type

This fixes the problem by using the UINT64_C macro from <inttypes.h> to
write a 64-constant.