P2P: Use hardcoded idle timeout of 10 seconds in P2P client role

P2P: Use hardcoded idle timeout of 10 seconds in P2P client role

The p2p_group_idle configuration parameter is much more useful for
GO role, so use a separate hardcoded value of 10 seconds in P2P
client role. In practice, this means that the P2P client role will
automatically tear down the group when the GO tears down the group.

The 10 second timeout is enough to recover from temporary disconnections
without unnecessary tearing down the group if the GO is still present
and allows the client to connect.

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