bug fixes from Fujitsu (bug 24)

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bug 24

Ttile:
The last line "multicast_group = multicast_group" is hard
to understand. The local variable should be different name
than the global variable.

Bug Location:
const char *multicast_group_list[MULTICAST_LINK_NUM_GROUPS] = {
  "239.0.0.161",
  "239.0.0.162",
  "239.0.0.163",
  "239.0.0.164"
};
:
:
void multicast_link_start(void (*rx_handlerP) (unsigned int, char *),
                          unsigned char multicast_group, char *multicast_ifname)
{
  rx_handler = rx_handlerP;
  multicast_group = multicast_group;

Note:
Detected by CppCheck
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