Restore batching in LinkUnqueue, originally added in commit 5b47e8c6 #584

Job	Run time
build (gcc, vanilla)	7m 32s
build (gcc, dpdk)	8m 19s
build (gcc, dpdk-light)	10m 38s
build (gcc, netmap)	7m 39s
build (gcc, vanilla-nopool)	7m 8s
build (gcc, dpdk-flow-dynamic)	8m 39s
build (clang, vanilla)	11m 6s
build (clang, dpdk)	12m 9s
build (clang, dpdk-light)	13m 45s
build (clang, netmap)	10m 43s
build (clang, vanilla-nopool)	10m 48s
build (clang, dpdk-flow-dynamic)	11m 52s
mirror	34s
	2h 0m 52s

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