net: qualcomm: rmnet: Implement ndo_get_iflink

This makes it easier to find out the parent dev.

Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Cc: Dan Williams <dcbw@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>