Due to a characteristic on ONTAP devices, the volume extend
operation has a max resize size limited by underlying LUN's
geometry, so the support for extend online volumes was
disabled.
This patch fixes it by allowing a volume (attached or not)
to be extended up to 16TB, which is the max LUN size
supported by ONTAP.
NFS online_extend_support is still disabled due to a bug [0]
found on the generic implementation for NFS driver, which
ONTAP NFS driver relies on.
Closes-Bug: #1874134
[0] https://bugs.launchpad.net/cinder/+bug/1870367
Change-Id: I2812d71b23f27fe8be4e9a757094867f71b1afa2
510613e135