NFC: Set active target upon DEP up event reception

As we can potentially get DEP up events without having sent a netlink
command, we need to set the active target properly from dep_link_is_up.
Spontaneous DEP up events can come from devices that detected an active
p2p target. In that case there is no need to call the netlink DEP up
command as the link is already up and running.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>