Increase initial group key handshake retransmit timeout to 500 ms

Increase initial group key handshake retransmit timeout to 500 ms

The 100 ms timeout on retransmitting group key message can be too short
for stations that are in power save mode or if there is a large number
of association stations. While the retransmission of the EAPOL-Key frame
should allow this to be recovered from, it is useful to avoid
unnecessary frames to save soem CPU and power.

Signed-hostap: Jouni Malinen <j@w1.fi>