selftests: mptcp: join: fix 'implicit EP' test

mptcp_join 'implicit EP' test currently fails when using ip mptcp:

$ ./mptcp_join.sh -iI
<snip>
001 implicit EP    creation[fail] expected '10.0.2.2 10.0.2.2 id 1 implicit' found '10.0.2.2 id 1 rawflags 10 '
Error: too many addresses or duplicate one: -22.
                   ID change is prevented[fail] expected '10.0.2.2 10.0.2.2 id 1 implicit' found '10.0.2.2 id 1 rawflags 10 '
                   modif is allowed[fail] expected '10.0.2.2 10.0.2.2 id 1 signal' found '10.0.2.2 id 1 signal '

This happens because of two reasons:
- iproute v6.3.0 does not support the implicit flag, fixed with
  iproute2-next commit 3a2535a41854 ("mptcp: add support for implicit
  flag")
- pm_nl_check_endpoint wrongly expects the ip address to be repeated two
  times in iproute output, and does not account for a final whitespace
  in it.

This fixes the issue trimming the whitespace in the output string and
removing the double address in the expected string.

Fixes: 34aa6e3 ("selftests: mptcp: add ip mptcp wrappers")
Signed-off-by: Andrea Claudi <[email protected]>

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

@@ -847,10 +847,11 @@ pm_nl_check_endpoint()
 	fi
 
 	if [ $ip_mptcp -eq 1 ]; then
+		# get line and trim trailing whitespace
 		line=$(ip -n $ns mptcp endpoint show $id)
+		line="${line% }"
 		# the dump order is: address id flags port dev
-		expected_line="$addr"
-		[ -n "$addr" ] && expected_line="$expected_line $addr"
+		[ -n "$addr" ] && expected_line="$addr"
 		expected_line="$expected_line $id"
 		[ -n "$_flags" ] && expected_line="$expected_line ${_flags//","/" "}"
 		[ -n "$dev" ] && expected_line="$expected_line $dev"