The SRP-6 specifications clearly say, that v and s are only to be
calculated on registering a user and changing his password; calculating
them on every login is plain waste.
CHECK_PACKET_SIZE was pretty error prone; once it was forgotten mangosd
could crash due to the asserts in ByteBuffer.h. That was exploitable by
malicious players.
Furthermore, there were duplicate checks: Additionally to
CHECK_PACKET_SIZE, the ByteBuffer assertions keept an eye
on not exceeding the packet boundaries - just to crash the server for
sure in such a case.
To prevent memory leaks or other undesirable states, please read in
every handler all variables _before_ doing any concrete handling.
