mptcp: deduplicate error paths on endpoint creation

mptcp: deduplicate error paths on endpoint creation

[ Upstream commit 976d302fb6165ad620778d7ba834cde6e3fe9f9f ]

When endpoint creation fails, we need to free the newly allocated
entry and eventually destroy the paired mptcp listener socket.

Consolidate such action in a single point let all the errors path
reach it.

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: ad2171009d96 ("mptcp: fix locking for in-kernel listener creation")
Signed-off-by: Sasha Levin <sashal@kernel.org>