When the parameter --rekey-plaintext is used, the rekey 4-way handshake
itself should be sent in plaintext. But possible EAPOL Request frames,
which ask the AP for a new 4-way handshake, should ideally still be sent
using encryption.
This patch assures that EAPOL (Rekey) Request frames are always sent
encrypted, even when --rekey-plaintext is used.