ibacm: Assign a provider to a port.

ibacm: Assign a provider to a port.

The assignment is based on a port's subnet_prefix. It is
assumed that all ports on a subnet partition should be
managed by one provider. The assignment is done through
the configuration file.

Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>