Get rid of netconf session preferences after connect
Memory usage improvement for sal-netconf-connector: The preferences object was
kept inside the data broker during the entire lifetime of a netconf connector.
This is not necessary as it only needs 3 boolean values from it.
+ intern String representation of capabilities written into datastore.
Change-Id: I46363a3dc079350ccb1db4840b31fdd5342798d3
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>
(cherry picked from commit
ed824b6afc20ad44f0fc0f955747e715d1fc90a0)