gw/netstat_once is a SAP Parameter attribute which is used to control Get own IP addresses only during startup 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 .
When you start up the gateway, all of your own IP addresses are
determined with the 'netstat' command and saved internally. This is
necessary to be able to establish whether a program must be started
locally or remotely.
There are high-availability solutions in which IP addresses can wander
from one host to another. That is, the entries that are read when the
gateway was started may no longer be valid. In this case, the current
configuration must always be read when performing the test for a local
IP address. To activate this mechanism, this profile parameter must be
set to 0.
A default value of 1 means that the configuration is read only once
during start up.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.