MINOR: buffers: split b_force_xfer() into b_cpy() and b_force_xfer()

Split the b_force_xfer() into b_ncat() and b_force_xfer().

The previous b_force_xfer() implementation was basically a copy with a
b_del on the src buffer. Keep this implementation to make b_ncat(), and
just call b_ncat() + b_del() into b_force_xfer().
1 file changed