Phonet: set the pipe handle using setsockopt

This provides flexibility to set the pipe handle
using setsockopt. The pipe can be enabled (if disabled) later
using ioctl.

Signed-off-by: Hemant Ramdasi <hemant.ramdasi@stericsson.com>
Signed-off-by: Dinesh Kumar Sharma <dinesh.sharma@stericsson.com>
Acked-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>