controld: fix memory leak
    
    Compile with -fsanitize=address unveils the following memory leak:
    
    ==1175==ERROR: LeakSanitizer: detected memory leaks
    
    Direct leak of 216 byte(s) in 3 object(s) allocated from:
        #0 0x7f0881809b17 in calloc (/lib64/libasan.so.6+0xaeb17)
        #1 0x55b3f110bc78 in send_protocol /builddir/devel/dlm/dlm_controld/daemon_cpg.c:1872
    
    SUMMARY: AddressSanitizer: 216 byte(s) leaked in 3 allocation(s).
    
    This patch free's the allocated buffer in send_protocol which should be
    copied in a different buffer by _send_message() already.