Check IPv6 address after processing HBH

[thvdveld]

Now, the destination address of the IP packet is checked if it is part of the interface addresses or the multicast addresses, only after processing the hop-by-hop header, as this header must be processed by every node.

1. I modified the has_multicast_group function to also check IPv6 multicast addresses, such as the ALL_NODES, ALL_RPL_NODES (only when using RPL) and the IPv6 solicited address.
2. For some HBH options, an ICMPv6 parameter problem must be transmitted RFC2460 Section 4.2. In some cases even when the destination address is a multicast address. Therefore also did point (3).
3. ICMPv6 messages were not transmitted when the destination address was a multicast address. I am not sure why we did it like that. When the destination address is multicast, I use the first IPv6 address from the interface. The selection of the correct IPv6 source address is something that still needs work in smoltcp.

RFC8200 Section 4 says the following about hop-by-hop headers:

Extension headers (except for the Hop-by-Hop Options header) are not
processed, inserted, or deleted by any node along a packet's delivery
path, until the packet reaches the node (or each of the set of nodes,
in the case of multicast) identified in the Destination Address field
of the IPv6 header.

Therefore, when an hop-by-hop extension is present, we should process it. Then we check if the packet reached its destination. If not, we discard the packet if we are not using a routing protocol. In case of RPL, we route the packet to the correct next node.

[codecov]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (8a86a5a) 79.74% compared to head (1001586) 79.74%.

Files	Patch %	Lines
src/iface/interface/ipv6.rs	86.66%	10 Missing ⚠️
src/iface/interface/mod.rs	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #861      +/-   ##
==========================================
- Coverage   79.74%   79.74%   -0.01%     
==========================================
  Files          78       78              
  Lines       28131    28165      +34     
==========================================
+ Hits        22433    22459      +26     
- Misses       5698     5706       +8     

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[whitequark]

@thvdveld Unfortunately this PR deals squarely with the bits of IPv6 I do not have a good understanding of.

[thvdveld]

@whitequark no problem!