Squash to "selftests: mptcp: pm_nl_ctl: always look for errors"

mptcp_join.sh selftest tries to add a bad endpoint on purpose ("ID
change is prevented") so it is normal to see this error:

   114 implicit EP
         creation                            [ ok ]
         mptcp_info subflows=1:1             [ ok ]
         mptcp_info add_addr=1:1             [ ok ]
   netlink error -22 (Invalid argument)
   ./pm_nl_ctl: bailing out due to netlink error[s]
         ID change is prevented              [ ok ]
         modif is allowed                    [ ok ]

We can mute the output because we expect an error.

We also need to edit the commit message to mention mptcp_join.sh
selftest also need to be modified, not just pm_netlink.sh.

Signed-off-by: Matthieu Baerts <[email protected]>

tools/testing/selftests/net/mptcp/mptcp_join.sh

@@ -3454,7 +3454,7 @@ endpoint_tests()
 		chk_mptcp_info subflows 1 subflows 1
 		chk_mptcp_info add_addr_signal 1 add_addr_accepted 1
 
-		pm_nl_add_endpoint $ns2 10.0.2.2 id 33
+		pm_nl_add_endpoint $ns2 10.0.2.2 id 33 2>/dev/null
 		pm_nl_check_endpoint "ID change is prevented" \
 			$ns2 10.0.2.2 id 1 flags implicit