BFD: Over child links of AE or LAG bundle, Micro BFD

BFD over child links of an AE or LAG bundle is supported. This feature provides a Layer 3 BFD liveness detection mechanism for child links of the Ethernet LAG interface. You can enable BFD to run on individual member links of the LAG to monitor the Layer 3 or Layer 2 forwarding capabilities of individual member links. These micro BFD sessions are independent of each other despite having a single client that manages the LAG interface. To enable failure detection for aggregated Ethernet interfaces, include the bfd-liveness-detection statement at the [edit interfaces aex aggregated-ether-options bfd-liveness-detection] hierarchy level.