Provide functions to determine if TLSv1.2 record protection is engaged.

Provide functions to determine if TLSv1.2 record protection is engaged.

Call these functions from code that needs to know if we've changed cipher
state and enabled record protection, rather than inconsistently checking
various pointers from other places in the code base. This also fixes a
minor bug where the wrong pointers are checked if we're operating with
AEAD.

ok inoguchi@ tb@