16 eves bug

Fix a 16 year old bug in the sorting routine for non-contiguous netmasks.
For masks of identical length rn_lexobetter() did not stop on the
first non-equal byte. This leads rn_addroute() to not detecting
duplicate entries and thus we might create a very long list of masks
to check for each node.
This can have a huge impact on IPsec performance, where non-contiguous
masks are used for the flow lookup. In a setup with 1300 flows we
saw 400 duplicate masks and only a third of the expected throughput.

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