SUNRPC: Pass a family argument to svc_register()

The sv_family field is going away.  Instead of using sv_family, have
the svc_register() function take a protocol family argument.

Since this argument represents a protocol family, and not an address
family, this argument takes an int, as this is what is passed to
sock_create_kern().  Also make sure svc_register's helpers are
checking for PF_FOO instead of AF_FOO.  The value of [AP]F_FOO are
equivalent; this is simply a symbolic change to reflect the semantics
of the value stored in that variable.

sock_create_kern() should return EPFNOSUPPORT if the passed-in
protocol family isn't supported, but it uses EAFNOSUPPORT for this
case.  We will stick with that tradition here, as svc_register()
is called by the RPC server in the same path as sock_create_kern().

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>