phonet/pep: refuse to enable an unbound pipe

In the Linux kernel, the following vulnerability has been resolved:

phonet/pep: refuse to enable an unbound pipe

This ioctl() implicitly assumed that the socket was already bound to

a valid local socket name, i.e. Phonet object. If the socket was not

bound, two separate problems would occur:

1) We'd send an pipe enablement request with an invalid source object.

2) Later socket calls could BUG on the socket unexpectedly being

connected yet not bound to a valid object.