docs: nf_flowtable: fix compilation and warnings

... cannot be used in block quote, it breaks compilation, remove it.

Fix warnings due to missing blank line such as:

net-next/Documentation/networking/nf_flowtable.rst:142: WARNING: Block quote ends without a blank line; unexpected unindent.

Fixes: 143490cde566 ("docs: nf_flowtable: update documentation with enhancements")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

docs: nf_flowtable: update documentation with enhancements

This patch updates the flowtable documentation to describe recent
enhancements:

- Offload action is available after the first packets go through the
classic forwarding path.
- IPv4 and IPv6 are supported. Only TCP and UDP layer 4 are supported at
this stage.
- Tuple has been augmented to track VLAN id and PPPoE session id.
- Bridge and IP forwarding integration, including bridge VLAN filtering
support.
- Hardware offload support.
- Describe the [OFFLOAD] and [HW_OFFLOAD] tags in the conntrack table
listing.
- Replace 'flow offload' by 'flow add' in example rulesets (preferred
syntax).
- Describe existing cache limitations.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

docs: nf_flowtable: fix typo.

"mailined" should be "mainlined."

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

docs: networking: convert nf_flowtable.txt to ReST

- add SPDX header;
- adjust title markup;
- mark code blocks and literals as such;
- add notes markups;
- adjust identation, whitespaces and blank lines;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>