Increase the default min-xthin-nodes to 8
Increase the default min-xthin-nodes to 8

By increasing the min-xthin-nodes count from 4 to 8 we can increase
the connectedness of the XTHIN network significantly and further
protect against any attempt to partition the BU network of nodes by
some sort of sybil attack.  Furthermore we also increase the default
outbound nodes to 12 to ensure we also keep the current value of 4
for other types of nodes.  In short we increase the number of XTHIN
outbound nodes by 4 but keep other outbound nodes with the same count.

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