default or selected kernelversion does not have config value CONFIG_BNX2X_VXLAN.
Result is shown for kernelversion 5.4.33

Virtual eXtensible Local Area Network support

configname: CONFIG_BNX2X_VXLAN

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Ethernet driver support
└─>Virtual eXtensible Local Area Network support
In linux kernel since version 4.3 (release Date: 2015-11-01)  
This enables hardward offload support for VXLAN protocol over the
NetXtremeII series adapters.
Say Y here if you want to enable hardware offload support for
Virtual eXtensible Local Area Network (VXLAN) in the driver.