Revert "net/mlx5: Kconfig: Fix MLX5_EN/VXLAN build issue"

This reverts commit 69976fb1.

We cannot select VXLAN when IPv4 support is disabled, that just gives
us additional build errors, including:

warning: (MLX5_CORE_EN) selects VXLAN which has unmet direct dependencies (NETDEVICES && NET_CORE && INET)
In file included from ../drivers/net/vxlan.c:36:0:
include/net/udp_tunnel.h: In function 'udp_tunnel_handle_offloads':
include/net/udp_tunnel.h:112:9: error: implicit declaration of function 'iptunnel_handle_offloads' [-Werror=implicit-function-declaration]
  return iptunnel_handle_offloads(skb, type);
         ^~~~~~~~~~~~~~~~~~~~~~~~

I'm sending a proper fix for the original bug in a separate patch.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>