net/smc: add pnet table namespace support

This patch adds namespace support to the pnet table code. Each network
namespace gets its own pnet table. Infiniband and smcd device pnetids
can only be modified in the initial namespace. In other namespaces they
can still be used as if they were set by the underlying hardware.

Signed-off-by: Hans Wippel <hwippel@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>