Fix Cython warnings

Fixes
```
warning: afs/_util.pyx:15:5: Function 'pioctl_read' previously declared as 'private'
warning: afs/_util.pyx:29:5: Function 'pioctl_write' previously declared as 'private'
warning: afs/_pts.pyx:115:8: Unreachable code
warning: afs/_pts.pyx:130:8: Unreachable code
afs/_pts.c: In function ‘__pyx_pf_3afs_4_pts_3PTS___cinit__’:
afs/_pts.c:2999:56: warning: ‘__pyx_v_sc’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     (__pyx_v_serverconns[__pyx_v_i]) = rx_NewConnection((__pyx_v_info.hostAddr[__pyx_v_i]).sin_addr.s_addr, (__pyx_v_info.hostAddr[__pyx_v_i]).sin_port, PRSRV, __pyx_v_sc, __pyx_t_9);
                                                        ^
```