nvmf: Limit namespace character device I/O size

Set si_iosize_max for namespace character devices matching the fix
from commit 125ec0e307.

Sponsored by:	Chelsio Communications

sys/dev/nvmf/host/nvmf_ns.c

@@ -398,6 +398,7 @@ nvmf_init_ns(struct nvmf_softc *sc, uint32_t id,
 	    device_get_nameunit(sc->dev), id);
 
 	ns->cdev->si_flags |= SI_UNMAPPED;
+	ns->cdev->si_iosize_max = sc->max_xfer_size;
 
 	return (ns);
 fail: