Handle new representation of abstract UDS paths.
Handle new representation of abstract UDS paths.

When abstract unix domain socket paths are displayed in
/proc/net/unix, Linux historically emitted null bytes as padding at
the end of the path. Newer versions of Linux (v4.9,
e7947ea770d0de434d38a0f823e660d3fd4bebb5) display these as '@'
characters.

Update proc_net_unix test to handle both version of the padding.

PiperOrigin-RevId: 266230200

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor