s3: Fix bug 8009 - net rap session cannot get username

s3: Fix bug 8009 - net rap session cannot get username

Looking in [MS-RAP].pdf - these strings are always 4 bytes as an
offset in the rparam area, the string length is the size in the rdata area.
Se we must always return we have consumed 4 param bytes.
(cherry picked from commit dd2e6fde0ab2e929b108c22244aac746e036a22c)