ktls: Add tests for receiving corrupted or invalid records.

These should all trigger errors when reading from the socket.

Tests include truncated records (socket closed early on the other
side), corrupted records (bits flipped in explicit IVs, ciphertext, or
MAC), invalid header fields, and various invalid record lengths.

Reviewed by: markj
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D37373