s390/net: add Thorsten Winkler as maintainer

Thank you Wenjia for your support, welcome Thorsten!
Acked-by: Wenjia Zhang <wenjia@linux.ibm.com>
Acked-by: Thorsten Winkler <twinkler@linux.ibm.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

MAINTAINERS

@@ -18962,7 +18962,7 @@ F:	drivers/iommu/s390-iommu.c
 
 S390 IUCV NETWORK LAYER
 M:	Alexandra Winter <wintera@linux.ibm.com>
-M:	Wenjia Zhang <wenjia@linux.ibm.com>
+M:	Thorsten Winkler <twinkler@linux.ibm.com>
 L:	linux-s390@vger.kernel.org
 L:	netdev@vger.kernel.org
 S:	Supported
@@ -18981,7 +18981,7 @@ F:	arch/s390/mm
 
 S390 NETWORK DRIVERS
 M:	Alexandra Winter <wintera@linux.ibm.com>
-M:	Wenjia Zhang <wenjia@linux.ibm.com>
+M:	Thorsten Winkler <twinkler@linux.ibm.com>
 L:	linux-s390@vger.kernel.org
 L:	netdev@vger.kernel.org
 S:	Supported