l4p: add ability to assign user-data to the stream

l4p: add ability to assign user-data to the stream

Add ability for the user to assign user provided data to the stream.
Right now this user provided 64-bit value is passed as a parameter
for lookup4/lookup6 callbacks.
Another change: change interpretation of lookup4()/lookup6() return value:
<  0: error code (existing behaviour).
== 0: success, TLDK will update L3 header src/dst addresses based on
      tldk dev values (existing behaviour).
>  0: success, TLDK will not update L3 header src/dst addresses, will
      rely on user provided values.

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Change-Id: I32521422e0372d79c4b2781dd6fc9740e4ca93ab