netlink: specs: mptcp: fix missing doc

Two operations didn't have a small description. It looks like something
that has been missed in the original commit introducing this file.

Replace the two 'todo' by a small and simple description: Create/Destroy
subflow.

Fixes: bc8aeb2 ("Documentation: netlink: add a YAML spec for mptcp")
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>

Author: matttbe

Documentation/netlink/specs/mptcp_pm.yaml

@@ -375,7 +375,7 @@ operations:
            - loc-id
     -
       name: subflow-create
-      doc: todo
+      doc: Create subflow
       attribute-set: attr
       dont-validate: [ strict ]
       flags: [ uns-admin-perm ]
@@ -387,7 +387,7 @@ operations:
             - addr-remote
     -
       name: subflow-destroy
-      doc: todo
+      doc: Destroy subflow
       attribute-set: attr
       dont-validate: [ strict ]
       flags: [ uns-admin-perm ]