Bluetooth: Use default RFC values if none received

A well-behaved remote device should always send a reconfiguration and
flow control (RFC) option in the configuration response when using
ERTM or Streaming mode.  By using default RFC option values, the
configuration code can avoid using uninitialized data.

Change-Id: I8f9ef687b694d0b34c6d65d40b934bc7946d515e
Signed-off-by: Mat Martineau <mathewm@codeaurora.org>