[SRU][B:linux-azure-4.15][PULL v2] hv_netvsc: Add XDP support

[William Breathitt Gray]

Changes in v2:
 - Merge conflicts resolved involving 'hash_info' introduction in the
   following patches:
   * "hv_netvsc: pass netvsc_device to receive callback"
   * "hv_netvsc: Add support for LRO/RSC in the vSwitch"
   * "hv_netvsc: Add XDP support"

BugLink: https://bugs.launchpad.net/bugs/1877654

[Impact]

Microsoft would like to request the following three patches in all releases supported on Azure:

351e1581395fc (“hv_netvsc: Add XDP support”)
12fa74383ed4d (“hv_netvsc: Update document for XDP support”)
184367dce4f7 (“hv_netvsc: Fix XDP refcnt for synthetic and VF NICs”)

These patches add support of XDP in native mode to the hv_netvsc driver, and
transparently sets the XDP program on the associated VF NIC as well.

[Regression Potential]

The backport to Bionic:linux-azure-4.15 required a lot of context
adjustments. Regression potentials are spread across a number of files
and drivers. Most adjustments were trivial, but the changes in
netvsc_drv.c should be kept an eye on. In particular, if a regression
occurs it will likely happen in the netvsc_alloc_recv_skb(),
netvsc_recv_callback(), or netvsc_devinfo_get() functions due to the
context difference of these areas compared to the original patch.

In general, Linux 4.15 was missing key code for XDP. As such, many
prelimary commit backports were required to pull in that support before
it could be added to hv_netvsc driver in the primary backports.

[Miscellaneous]

The 5.4 version is already released so we do not need to worry about
that series.

Backports of the "xdp: new XDP rx-queue info concept" patchset and "XDP
redirect memory return API" patchset patches are included to add support
for the XDP API:
https://patchwork.ozlabs.org/project/netdev/cover/151497504273.18176.10177133999720101758.stgit@firesoul/
https://patchwork.ozlabs.org/project/netdev/cover/152397622657.20272.10121948713784224943.stgit@firesoul/

William Breathitt Gray

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The following changes since commit 822cd876f23c1e6809e563c5c396216bdb131880:
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