net: ipa: save a copy of endpoint default config

All elements of the default endpoint configuration are used in the
code when programming an endpoint for use.  But none of the other
configuration data is ever needed once things are initialized.

So rather than saving a pointer to *all* of the configuration data,
save a copy of only the endpoint configuration portion.

This will eventually allow endpoint configuration to be modifiable
at runtime.  But even before that it means we won't keep a pointer
to configuration data after when no longer needed.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>