Bluetooth: Fix auto PHY update on connection

Since the PHY update complete event can be generated due to the
procedure being initiated by the peer, use a flag to
differentiate between local auto update initiated on connection
complete versus peer initiated anytime in the connection. This
is necessary to avoid repeated initiation of auto-update
procedures intended only to be issued on connection complete.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>