Rely on the kernel to check the ident for us.

The code path that uses the ping socket still keeps track of the
ident value in the packet. This is unnecessary because the ident
value is overwritten by the kernel when sending packets and is
checked by the kernel when receiving packets.

Instead just rely on the fact that the kernel checks the ident
value on received packets filters out non-matching replies.  This
allows us to remove the code that calls bind() and getsockname()
just to get the ident value from the socket.

Bug: 9469682
Change-Id: I5041316c6e5262a4de2b547c40bd77cfac29a5b9