net: ipv6: Allow connect to linklocal address from socket bound to vrf

Allow a process bound to a VRF to connect to a linklocal address.
Currently, this fails because of a mismatch between the scope of the
linklocal address and the sk_bound_dev_if inherited by the VRF binding:
    $ ssh -6 fe80::70b8:cff:fedd:ead8%eth1
    ssh: connect to host fe80::70b8:cff:fedd:ead8%eth1 port 22: Invalid argument

Relax the scope check to allow the socket to be bound to the same L3
device as the scope id.

This makes ipv6 linklocal consistent with other relaxed checks enabled
by commits 1ff23bee ("net: l3mdev: Allow send on enslaved interface")
and 7bb387c5 ("net: Allow IP_MULTICAST_IF to set index to L3 slave").

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>