default or selected kernelversion does not have config value CONFIG_VENDOR_SANGOMA.
Result is shown for kernelversion 5.4.123

Sangoma WANPIPE(tm) multiprotocol cards

modulename: sdladrv.ko

configname: CONFIG_VENDOR_SANGOMA

Linux Kernel Configuration
└─>Networking support
└─>Wan interfaces
└─>Sangoma WANPIPE(tm) multiprotocol cards
In linux kernel since version 2.6.12  
Driver for S514-PCI/ISA Synchronous Data Link Adapters (SDLA).

WANPIPE from Sangoma Technologies Inc. <http://www.sangoma.com/>
is a family of intelligent multiprotocol WAN adapters with data
transfer rates up to 4Mbps. Cards support:

- X.25, Frame Relay, PPP, Cisco HDLC protocols.

- API for protocols like HDLC (LAPB), HDLC Streaming, X.25,
Frame Relay and BiSync.

- Ethernet Bridging over Frame Relay protocol.

- MULTILINK PPP

- Async PPP (Modem Dialup)

The next questions will ask you about the protocols you want
the driver to support.

If you have one or more of these cards, say M to this option;
and read Documentation/networking/wanpipe.txt.

To compile this driver as a module, choose M here: the
module will be called wanpipe.

source code:
drivers/net//wan/