why "ls -al" does not show file size info in /dev/socket directory?
Sockets and pipes represent Unix' way of inter process communication, and a communication channel has no point in having a size. Sockets are thus not seekable as in go to position x in the file.

Linux (which Android makes use of) has 7 file types:


Regular Files
Directories
Character  Device Files
Block Device Files
Local Domain Sockets
Named Pipes
Symbolic Links


See more here