Add more crypto toolbox tests, plus minor fix in smp_keys.cc

This code extracts two new functions, smp_calculate_ltk_to_link_key
and smp_calculate_link_key_to_ltk, in order to test them.
Also use modulo operator to compute modulo in smp_calculate_g2.
Plus remove unused function definitions in smp_int.h, that were probably
previously used for testing.


Test: added and updated CryptoToolboxTest
Change-Id: Ia84f72af666fc8e34f887b65b07208bc786bf2e0