add new_keys argument to esp_setup_keys() in preparation for supporting GlobalProtect ESP

add new_keys argument to esp_setup_keys() in preparation for supporting GlobalProtect ESP

The existing ESP key setup code can be almost entirely reused for
GlobalProtect ESP, except for the fact that esp_setup_keys() always
overwrites the secret keys with new random keys.

Since GlobalProtect ESP always uses keys provided by the server, a new
argument is added to esp_setup_keys() to make this behavior optional.
The Juniper-specific code in oncp.c calls it with new_keys=1 in order
to explicitly request it.

Signed-off-by: Daniel Lenski <dlenski@gmail.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>