SUNRPC display xprt's main value in sysfs's xprt_info

Display in sysfs in the information about the xprt if this is a
main transport or not.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>