doc: add RIB and FIB into the API index

Add RIB/FIB library into the API doxygen index.
Move LPM/LPM6 under separate section "routing".

Fixes: 5a5793a5ff ("rib: add RIB library")
Fixes: f7e861e21c ("rib: support IPv6")
Fixes: 39e9272484 ("fib: add FIB library")
Fixes: 40d41a8a7b ("fib: support IPv6")
Cc: stable@dpdk.org

Signed-off-by: Vladimir Medvedkin <vladimir.medvedkin@intel.com>

doc/api/doxy-api-index.md

@@ -108,8 +108,6 @@ The public API headers are grouped by topics:
   [GRO]                (@ref rte_gro.h),
   [GSO]                (@ref rte_gso.h),
   [frag/reass]         (@ref rte_ip_frag.h),
-  [LPM IPv4 route]     (@ref rte_lpm.h),
-  [LPM IPv6 route]     (@ref rte_lpm6.h),
   [VXLAN]              (@ref rte_vxlan.h)
 
 - **QoS**:
@@ -117,6 +115,14 @@ The public API headers are grouped by topics:
   [scheduler]          (@ref rte_sched.h),
   [RED congestion]     (@ref rte_red.h)
 
+- **routing**:
+  [LPM IPv4 route]     (@ref rte_lpm.h),
+  [LPM IPv6 route]     (@ref rte_lpm6.h),
+  [RIB IPv4]           (@ref rte_rib.h),
+  [RIB IPv6]           (@ref rte_rib6.h),
+  [FIB IPv4]           (@ref rte_fib.h),
+  [FIB IPv6]           (@ref rte_fib6.h)
+
 - **hashes**:
   [hash]               (@ref rte_hash.h),
   [jhash]              (@ref rte_jhash.h),