IB/core: Do not require CAP_NET_ADMIN for packet sniffing

IB/core: Do not require CAP_NET_ADMIN for packet sniffing

In the Ethernet/TCP world, CAP_NET_RAW is sufficient to allow a program
to listen to all incoming packets on a specific interface, and the
higher CAP_NET_ADMIN is required to set the interface into promiscuous
mode.  We want to emulate that same basic division of privilege in the
RDMA stack, so when dealing with Raw Ethernet QPs, allow apps with
CAP_NET_RAW to listen to all incoming flows (and direct them as they see
fit in their own listen stream).  Do not require CAP_NET_ADMIN just to
listen to traffic already incoming.  Reserve CAP_NET_ADMIN if we attempt
to set promiscuous mode.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>