conf: multiple NULL-pointer dereferences in StreamTcpInitConfig

conf: multiple NULL-pointer dereferences in StreamTcpInitConfig

There are several NULL-pointer derefs in StreamTCPInitConfig. All of them happen because ConfGet returns 1 even if the value is NULL(due to misconfiguration for example).
This commit introduces a new function "ConfGetValue". It adds return values for NULL-pointer to ConfGet and could be used as a replacement for ConfGet.

Note: Simply modify ConfGet might not be a good idea, because there are some places where ConfGet should return 1 even if "value" is NULL. For example if ConfGet should get a Config-Leave in the yaml-hierarchy.

Bug: 2354