memory: avoid exercising the reclaimers for oversized requests
memory: avoid exercising the reclaimers for oversized requests

If someone allocates more memory than exists on the shard, we can fail
the request immediately, rather than evicting all evictable memory first.

kjniemi/seastar,dreamsxin/seastar,cloudius-systems/seastar,syuu1228/seastar,avikivity/seastar,avikivity/seastar,dreamsxin/seastar,cloudius-systems/seastar,kjniemi/seastar,avikivity/seastar,scylladb/seastar,dreamsxin/seastar,cloudius-systems/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,scylladb/seastar,kjniemi/seastar