gw/use_udp is a SAP Parameter attribute which is used to control enable/disable UDP port information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Specifies whether a datagram port (UDP) is opened alongside the TCP/IP
port. This datagram port is needed to receive connections from old
gateways (Release 2.x).
See SAP Parameter Documentation for full SAP documentation for this profile parameter.