net/mlx5: update E-Switch VXLAN netlink routines

net/mlx5: update E-Switch VXLAN netlink routines

This part of patchset updates Netlink exchange routine. Message
sequence numbers became not random ones, the multipart reply messages
are supported, not propagating errors to the following socket calls,
Netlink replies buffer size is increased to MNL_SOCKET_BUFFER_SIZE
and now is preallocated at context creation time instead of stack
usage. This update is needed to support Netlink query operations.

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