[babel] info-model: DTLS config parameters

["STARK, BARBARA H" <[e-mail]>]

I was reviewing the minutes from Prague, and saw they indicated we didn't have resolution on whether certain DTLS configuration parameters should be global or at the interface level.
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The current revision has the following global parameters:

   babel-dtls-enable:  Indicates whether the DTLS security mechanism is
      enabled (true) or disabled (false).  An implementation MAY choose
      to expose this parameter as read-only ("ro").

   babel-dtls-cert-types:  List of supported DTLS certificate types.
      Possible values include "X.509" and "RawPublicKey".
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And the following are at the interface level:

   babel-dtls-cached-info:  Indicates whether the cached_info extension
      is included in ClientHello and ServerHello packets.  The extension
      is included if the value is "true".  An implementation MAY choose
      to expose this parameter as read-only ("ro").

   babel-dtls-cert-prefer:  List of supported certificate types, in
      order of preference.  The values MUST be among those listed in the
      babel-dtls-cert-types parameter.  This list is used to populate
      the server_certificate_type extension in a Client Hello.  Values
      that are present in at least one instance in the babel-dtls-certs
      object of a referenced babel-dtls instance and that have a non-
      empty babel-cert-private-key will be used to populate the
      client_certificate_type extension in a Client Hello.


Please let me know if you disagree with this set of global/interface DTLS config parameters.
Barbara