log.set_level(): Return current flags

Make log.set_level() return the flags that were set before setting
the flags passed as argument.

Support None as flags argument, in which case it doesn't change
anything and only returns the currently set flags.

Signed-off-by: Jan Lindemann <jan@janware.com>

tools/python/jwutils/log.py

@@ -235,9 +235,12 @@ def set_level(level_: str) -> None: # export
         return
     _level = level_
 
-def set_flags(flags_: str) -> None: # export
+def set_flags(flags: str|None) -> None: # export
     global _flags
-    _flags = set(flags_.split(','))
+    ret = ','.join(_flags)
+    if _flags is not None:
+        _flags = set(flags.split(','))
+    return ret
 
     #syslog
     #console