ssize_t is not C compliant

[cochicde]

Description

For sending and receiving packets (UDP and TCP) the result used in the stack is of type ssize_t, which is a posix type, not a standard C type. This comes from using the functions send, recv and similars from posix, which returns these types.

But this comes to a problem to other architectures. For now, the workaround is to define ssize_t normally to int, in the architecture.h file. But in the stack itself (anywhere outside the arch folder) this ssize_t should be changed, maybe to int, but I'm not sure about it

Background Information / Reproduction Steps

Checklist

Please provide the following information:

• open62541 Version (release number or git tag): master branch
• Other OPC UA SDKs used (client or server): none
• Operating system: Any non-posix
• Logs (with UA_LOGLEVEL set as low as necessary) attached: non applicable
• Wireshark network dump attached: non applicable
• Self-contained code example attached: non applicable
• Critical issue: no