net/mlx5: add E-Switch VXLAN encapsulation rules

net/mlx5: add E-Switch VXLAN encapsulation rules

VXLAN encap rules are applied to the VF ingress traffic and have the
VTEP as actual redirection destinations instead of outer PF.
The encapsulation rule should provide:
- redirection action VF->PF
- VF port ID
- some inner network parameters (MACs/IP)
- the tunnel outer source IP (v4/v6)
- the tunnel outer destination IP (v4/v6). Current
- VNI - Virtual Network Identifier

There is no direct way found to provide kernel with all required
encapsulatioh header parameters. The encapsulation VTEP is created
attached to the outer interface and assumed as default path for
egress encapsulated traffic. The outer tunnel IP address are
assigned to interface using Netlink, the implicit route is
created like this:

  ip addr add <src_ip> peer <dst_ip> dev <outer> scope link

Peer address provides implicit route, and scode link reduces
the risk of conflicts. At initialization time all local scope
link addresses are flushed from device (see next part of patchset).

The destination MAC address is provided via permenent neigh rule:

  ip neigh add dev <outer> lladdr <dst_mac> to <dst_ip> nud permanent

At initialization time all neigh rules of this type are flushed
from device (see the next part of patchset).

Suggested-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>