detect/dataset: skip adding localstatedir if fullpath is provided

[norg]

When the option to set a full path is enabled and a full path is provided, skip adding the prefix (based on localstatedir) to the directory since it would be unexpected and unwanted by a user.

Ticket: 7083

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Link to ticket: https://redmine.openinfosecfoundation.org/issues/7083

Describe changes:

• When a user enables the option to provide a full path for a dataset, the prefix (based on localstatedir) should not be added since it doesn't make much sense to add that prefix on a provided full path
• This commit adds a check to skip the prefix addition in that case

Provide values to any of the below to override the defaults.

• To use an LibHTP, Suricata-Verify or Suricata-Update pull request, link to the pull request in the respective _BRANCH variable.
• Leave unused overrides blank or remove.

SV_REPO= SV_BRANCH= SU_REPO= SU_BRANCH= LIBHTP_REPO= LIBHTP_BRANCH=