Revisit: Allow Socket API applications to use IP multicast communication by joining and leaving Multicast groups

This ticket was cloned from the linked ticket since I am not happy with what has been implemented and I think this should be checked again.

There are at least two resource stakeholders for multicast groups:

1. The EIP stack (different demands fro adapter and scanner)
2. The socket API

There is a global pool of multcast groups in LWIP which we have to dimension. The size of this pool must be at least the sum of at 1 & 2. This does not seem to be the case. Please investigate. This should not work or is at least unclear.

A shared pool of multicast addresses for multiple users was/is not supported by the EIP core, additional measures are required for proper system dimensioning and partitioning of the globbal pool between the users. Implemented concept is not clear to me.

I also doubt that it is was  such a good idea to duplicate the default initializers from g_tLwip_PoolConfig_Small as magic values. Deep lwIP knowledge is required to understand these parameters and I see no benefit of having the hardcoded defaults copied.