net: qualcomm: rmnet: Rename real_dev_info to port

Make it similar to drivers like ipvlan / macvlan so it is easier to read.

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