Restore batching in LinkUnqueue, originally added in commit 5b47e8c6 #585

Job	Run time
build (gcc, vanilla)	7m 17s
build (gcc, dpdk)	8m 32s
build (gcc, dpdk-light)	10m 31s
build (gcc, netmap)	7m 26s
build (gcc, vanilla-nopool)	7m 29s
build (gcc, dpdk-flow-dynamic)	8m 11s
build (clang, vanilla)	11m 14s
build (clang, dpdk)	11m 46s
build (clang, dpdk-light)	14m 17s
build (clang, netmap)	10m 56s
build (clang, vanilla-nopool)	10m 41s
build (clang, dpdk-flow-dynamic)	12m 16s
mirror	42s
	2h 1m 18s

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