Merge branch 'net-hdlc_fr-improve-fr_rx-and-add-support-for-any-ethertype'

Merge branch 'net-hdlc_fr-improve-fr_rx-and-add-support-for-any-ethertype'

Xie He says:

====================
net: hdlc_fr: Improve fr_rx and add support for any Ethertype

The main purpose of this series is the last patch. The previous 4 patches
are just code clean-ups so that the last patch will not make the code too
messy. The patches must be applied in sequence.

The receiving code of this driver doesn't support arbitrary Ethertype
values. It only recognizes a few known Ethertypes when receiving and drops
skbs with other Ethertypes.

However, the standard document RFC 2427 allows Frame Relay to support any
Ethertype values. This series adds support for this.

Change from v6:
Remove the explanation about why only a 2-byte address field is accepted
because I think it is inadequate and unnecessary.

Change from v5:
Small fix to the commit messages.

Change from v4:
Drop the change related to the stats.rx_dropped count.
Improve the commit message by stating why only a 2-byte address field
is accepted.

Change from v3:
Split the last patch into 2 patches.
Improve the commit message about the stats.rx_dropped count.

Change from v2:
Small fix to the commit messages.

Change from v1:
Small fix to the commit messages.
====================

Link: https://lore.kernel.org/r/20201031181043.805329-1-xie.he.0141@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>