MAINTAINERS: Add an entry for the net/slirp.c file

The file net/slirp.c should be listed in the SLIRP section, too.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

MAINTAINERS

@@ -1199,6 +1199,7 @@ SLIRP
 M: Jan Kiszka <jan.kiszka@siemens.com>
 S: Maintained
 F: slirp/
+F: net/slirp.c
 T: git git://git.kiszka.org/qemu.git queues/slirp
 
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