Fix broken chmod in open_logfile().

gcc (Debian 12.2.0-14) 12.2.0

sn_logfile.c:96:8: warning: passing argument 1 of 'fchmod' makes integer
  from pointer without a cast [-Wint-conversion]

fchmod() takes a file descriptor, not a pointer to FILE, so the call to
fchmod() always failed.  In order not to involve fileno(), just use
chmod(), which takes a pathname, which the function already knows.

src/sn_logfile.c

@@ -93,7 +93,7 @@ LogFILE=fopen(Logfile,"a");
 if(LogFILE==NULL)
   printf("Sniffit heartattack.. couldn't create/open logfile...\n"), exit(1);
 exit_func(logfile_exit);
-fchmod(LogFILE,  S_IWUSR|S_IRUSR);
+chmod(Logfile, S_IWUSR|S_IRUSR);
 print_logline("Sniffit session started.");
 printf("Sniffit Logging started.\n");
 }