maintainers: update for stable branches

[ upstream commit 4318cd2a4df1b05d252cdb05fb1e0a9dce378018 ]

Christian and Xueming are both already maintaining LTS releases.

Update the MAINTAINERS file to reflect this.

Signed-off-by: Kevin Traynor <ktraynor@redhat.com>

MAINTAINERS

@@ -73,6 +73,8 @@ T: git://dpdk.org/next/dpdk-next-pipeline
 Stable Branches
 M: Luca Boccassi <bluca@debian.org>
 M: Kevin Traynor <ktraynor@redhat.com>
+M: Christian Ehrhardt <christian.ehrhardt@canonical.com>
+M: Xueming Li <xuemingl@nvidia.com>
 T: git://dpdk.org/dpdk-stable
 
 Security Issues