Fix SHA-256-based KDF when using CCMP as the pairwise cipher

Fix SHA-256-based KDF when using CCMP as the pairwise cipher

IEEE 802.11r KDF uses key length in the derivation and as such, the PTK
length must be specified correctly. The previous version was deriving
using 512-bit PTK regardless of the negotiated cipher suite; this works
for TKIP, but not for CCMP. Update the code to use proper PTK length
based on the pairwise cipher.

This fixed PTK derivation for both IEEE 802.11r and IEEE 802.11w (when
using AKMP that specifies SHA-256-based key derivation). The fixed
version does not interoperate with the previous versions. [Bug 307]