mptcp: pm: mark missing address attributes

mptcp: pm: mark missing address attributes

mptcp_pm_parse_entry() will check if the given attribute is defined. If
not, it will return a generic error: "missing address info".

It might then not be clear for the userspace developer which attribute
is missing, especially when the command takes multiple addresses.

By using GENL_REQ_ATTR_CHECK(), the userspace will get a hint about
which attribute is missing, making thing clearer. Note that this is what
was already done for most of the other MPTCP NL commands, this patch
simply adds the missing ones.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>