ffserver: replace atoll() by strtoll()

this should make it easier to support ffserver with msvc
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffserver.c

@@ -4151,7 +4151,7 @@ static int parse_ffconfig(const char *filename)
         } else if (!av_strcasecmp(cmd, "MaxBandwidth")) {
             int64_t llval;
             get_arg(arg, sizeof(arg), &p);
-            llval = atoll(arg);
+            llval = strtoll(arg, NULL, 10);
             if (llval < 10 || llval > 10000000) {
                 ERROR("Invalid MaxBandwidth: %s\n", arg);
             } else