NLSR

I attempted to implement this, but operator==() should always be const. However, many of the participating methods for the data structures of the LSAs are not const, so they require constification, first. At some points this requires many steps of spot fixes, and in some places simple constification is not possible due to logical inconsistencies.

Achieving this will require more careful thought and possibly redesign of the LSA classes and their data structures.

https://gerrit.named-data.net/c/NLSR/+/7147 fixes NamePrefixList::operator== so that it compares names only, which is the behavior prescribed in a unit test comment.
This patch also simplifies the implementation of NamePrefixList type.
NamePrefixList type is now a fully sorted container, and the sort() method is deleted.

https://gerrit.named-data.net/c/NLSR/+/7167 splits test-lsa.cpp into three test suites, in preparation of further cleans in LSA test suites.