vxlan: vni filtering support on collect metadata device

This patch adds vnifiltering support to collect metadata device.

Motivation:
You can only use a single vxlan collect metadata device for a given
vxlan udp port in the system today. The vxlan collect metadata device
terminates all received vxlan packets. As shown in the below diagram,
there are use-cases where you need to support multiple such vxlan devices in
independent bridge domains. Each vxlan device must terminate the vni's
it is configured for.
Example usecase: In a service provider network a service provider
typically supports multiple bridge domains with overlapping vlans.
One bridge domain per customer. Vlans in each bridge domain are
mapped to globally unique vxlan ranges assigned to each customer.

vnifiltering support in collect metadata devices terminates only configured
vnis. This is similar to vlan filtering in bridge driver. The vni filtering
capability is provided by a new flag on collect metadata device.

In the below pic:
	- customer1 is mapped to br1 bridge domain
	- customer2 is mapped to br2 bridge domain
	- customer1 vlan 10-11 is mapped to vni 1001-1002
	- customer2 vlan 10-11 is mapped to vni 2001-2002
	- br1 and br2 are vlan filtering bridges
	- vxlan1 and vxlan2 are collect metadata devices with
	  vnifiltering enabled

┌──────────────────────────────────────────────────────────────────┐
│  switch                                                          │
│                                                                  │
│         ┌───────────┐                 ┌───────────┐              │
│         │           │                 │           │              │
│         │   br1     │                 │   br2     │              │
│         └┬─────────┬┘                 └──┬───────┬┘              │
│     vlans│         │               vlans │       │               │
│     10,11│         │                10,11│       │               │
│          │     vlanvnimap:               │    vlanvnimap:        │
│          │       10-1001,11-1002         │      10-2001,11-2002  │
│          │         │                     │       │               │
│   ┌──────┴┐     ┌──┴─────────┐       ┌───┴────┐  │               │
│   │ swp1  │     │vxlan1      │       │ swp2   │ ┌┴─────────────┐ │
│   │       │     │  vnifilter:│       │        │ │vxlan2        │ │
│   └───┬───┘     │   1001,1002│       └───┬────┘ │ vnifilter:   │ │
│       │         └────────────┘           │      │  2001,2002   │ │
│       │                                  │      └──────────────┘ │
│       │                                  │                       │
└───────┼──────────────────────────────────┼───────────────────────┘
        │                                  │
        │                                  │
  ┌─────┴───────┐                          │
  │  customer1  │                    ┌─────┴──────┐
  │ host/VM     │                    │customer2   │
  └─────────────┘                    │ host/VM    │
                                     └────────────┘

With this implementation, vxlan dst metadata device can
be associated with range of vnis.
struct vxlan_vni_node is introduced to represent
a configured vni. We start with vni and its
associated remote_ip in this structure. This
structure can be extended to bring in other
per vni attributes if there are usecases for it.
A vni inherits an attribute from the base vxlan device
if there is no per vni attributes defined.

struct vxlan_dev gets a new rhashtable for
vnis called vxlan_vni_group. vxlan_vnifilter.c
implements the necessary netlink api, notifications
and helper functions to process and manage lifecycle
of vxlan_vni_node.

This patch also adds new helper functions in vxlan_multicast.c
to handle per vni remote_ip multicast groups which are part
of vxlan_vni_group.

Fix build problems:
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Roopa Prabhu <roopa@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>