"too many open files" without doing anything

#### Version information:
go-ipfs version: 0.4.18-
Repo version: 7
System version: amd64/linux
Golang version: go1.11.1

#### Type:
Bug

#### Description:
I start my daemon and see this:

```
Swarm listening on /p2p-circuit
Swarm announcing /ip4/10.147.17.230/tcp/4001
Swarm announcing /ip4/10.147.20.230/tcp/4001
Swarm announcing /ip4/127.0.0.1/tcp/4001
Swarm announcing /ip4/191.249.146.196/tcp/17619
Swarm announcing /ip4/192.168.15.5/tcp/4001
Swarm announcing /ip6/2804:7f2:2080:2760:9e2a:70ff:fe8a:769/tcp/4001
Swarm announcing /ip6/2804:7f2:2080:2760:fce1:6fc7:5cdb:4739/tcp/4001
Swarm announcing /ip6/::1/tcp/4001
Swarm announcing /ip6/fc99:d06b:a6f9:f0:ab56::1/tcp/4001
API server listening on /ip4/0.0.0.0/tcp/5001
Gateway (readonly) server listening on /ip4/127.0.0.1/tcp/7070
Daemon is ready
2018/11/05 09:58:41 http: Accept error: accept tcp4 0.0.0.0:5001: accept4: too many open files; retrying in 5ms
2018/11/05 09:58:41 http: Accept error: accept tcp4 0.0.0.0:5001: accept4: too many open files; retrying in 10ms
09:58:56.900 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
2018/11/05 09:59:15 http: Accept error: accept tcp4 0.0.0.0:5001: accept4: too many open files; retrying in 5ms
2018/11/05 09:59:15 http: Accept error: accept tcp4 0.0.0.0:5001: accept4: too many open files; retrying in 10ms
09:59:27.073 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
09:59:31.985 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
09:59:31.987 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
09:59:31.989 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
09:59:31.991 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
09:59:31.992 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004163.ldb: too many open files engine.go:258
09:59:31.994 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004163.ldb: too many open files engine.go:258
09:59:45.244 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
09:59:45.247 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
09:59:45.248 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
09:59:53.314 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
10:00:01.211 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004159.ldb: too many open files engine.go:258
10:00:01.398 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004159.ldb: too many open files engine.go:258
10:00:01.504 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004160.ldb: too many open files engine.go:258
10:00:03.630 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
10:00:03.637 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
10:00:03.656 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004163.ldb: too many open files engine.go:258
10:00:05.864 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004157.ldb: too many open files engine.go:258
10:00:09.517 ERROR engine: open /home/fiatjaf/.ipfs/datastore/004166.ldb: too many open files engine.go:258
```

And it goes on forever.
The only command I've run is `ipfs files ls /`, but I don't know what my node is doing, if it is serving some files or what, maybe it is. Is it failing to accept a connection from my own cli?

I don't know, but this seems related to https://github.com/ipfs-shipyard/ipfs-companion/issues/614 and https://github.com/ipfs/go-ipfs/issues/5738