gobgp/lib: Remove usage of utils of "gobgpapi"
gobgp/lib: Remove usage of utils of "gobgpapi"

"gobgp/lib" can be independent from "gobgpapi" package, this patch
removes the usage of utility function "ToPathApi()" in this package.

Signed-off-by: IWASE Yusuke <bb80e84cc9f5a8f01385872ee89032beb5d4eba7@gmail.com>

fujita/gobgp,tamihiro/gobgp,a16/gobgp,a16/gobgp,fujita/gobgp,a16/gobgp,osrg/gobgp,osrg/gobgp,fujita/gobgp,j-kato/gobgp,a16/gobgp,tamihiro/gobgp,tamihiro/gobgp,a16/gobgp,j-kato/gobgp,osrg/gobgp,fujita/gobgp,tamihiro/gobgp,osrg/gobgp,j-kato/gobgp,a16/gobgp,a16/gobgp