net: mctp: provide a more specific tag allocation ioctl

Now that we have net-specific tags, extend the tag allocation ioctls
(SIOCMCTPALLOCTAG / SIOCMCTPDROPTAG) to allow a network parameter to be
passed to the tag allocation.

We also add a local_addr member to the ioc struct, to allow for a future
finer-grained tag allocation using local EIDs too. We don't add any
specific support for that now though, so require MCTP_ADDR_ANY or
MCTP_ADDR_NULL for those at present.

The old ioctls will still work, but allocate for the default MCTP net.
These are now marked as deprecated in the header.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>