page_frag_free() won't completely release the memory
allocated for the commands, the cache page must be explicitly
freed by calling __page_frag_cache_drain().

This bug can be easily reproduced by repeatedly
executing the following command on the initiator:

$echo 1 > /sys/devices/virtual/nvme-fabrics/ctl/nvme0/reset_controller

Signed-off-by: Maurizio Lombardi <redacted>
Reviewed-by: John Meneghini <redacted>

This came a long a number of times before, thanks for
fixing this.

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>