[fib algo][dxr] Optimize trie updating.
Don't rebuild in vain trie parts unaffected by accumulated incremental
RIB updates.
PR: 257965
Tested by: Konrad Kreciwilk
MFC after: 3 days
(cherry picked from commit b51f8bae570b4e908191a1dae9da38aacf8c0fab)