Merge branch 'vrf-allow-simultaneous-service-instances-in-default-and-other-VRFs'

Mike Manning says:

====================
vrf: allow simultaneous service instances in default and other VRFs

Services currently have to be VRF-aware if they are using an unbound
socket. One cannot have multiple service instances running in the
default and other VRFs for services that are not VRF-aware and listen
on an unbound socket. This is because there is no easy way of isolating
packets received in the default VRF from those arriving in other VRFs.

This series provides this isolation for stream sockets subject to the
existing kernel parameter net.ipv4.tcp_l3mdev_accept not being set,
given that this is documented as allowing a single service instance to
work across all VRF domains. Similarly, net.ipv4.udp_l3mdev_accept is
checked for datagram sockets, and net.ipv4.raw_l3mdev_accept is
introduced for raw sockets. The functionality applies to UDP & TCP
services as well as those using raw sockets, and is for IPv4 and IPv6.

Example of running ssh instances in default and blue VRF:

$ /usr/sbin/sshd -D
$ ip vrf exec vrf-blue /usr/sbin/sshd
$ ss -ta | egrep 'State|ssh'
State   Recv-Q   Send-Q           Local Address:Port       Peer Address:Port
LISTEN  0        128           0.0.0.0%vrf-blue:ssh             0.0.0.0:*
LISTEN  0        128                    0.0.0.0:ssh             0.0.0.0:*
ESTAB   0        0              192.168.122.220:ssh       192.168.122.1:50282
LISTEN  0        128              [::]%vrf-blue:ssh                [::]:*
LISTEN  0        128                       [::]:ssh                [::]:*
ESTAB   0        0           [3000::2]%vrf-blue:ssh           [3000::9]:45896
ESTAB   0        0                    [2000::2]:ssh           [2000::9]:46398

v1:
   - Address Paolo Abeni's comments (patch 4/5)
   - Fix build when CONFIG_NET_L3_MASTER_DEV not defined (patch 1/5)
v2:
   - Address David Aherns' comments (patches 4/5 and 5/5)
   - Remove patches 3/5 and 5/5 from series for individual submissions
   - Include a sysctl for raw sockets as recommended by David Ahern
   - Expand series into 10 patches and provide improved descriptions
v3:
   - Update description for patch 1/10 and remove patch 6/10
v4:
   - Set default to enabled for raw socket sysctl as recommended by David Ahern
v5:
   - Address review comments from David Ahern in patches 2-5
====================

Signed-off-by: David S. Miller <davem@davemloft.net>