SOLVED : Nmap may not work correctly on Windows Subsystem for Linux.

WSL NMAP Error:  

Warning: Nmap may not work correctly on Windows Subsystem for Linux.                                          For best performance and accuracy, use the native Windows build from https://nmap.org/download.html#windows.     

Couldn't open a raw socket. Error: Permission denied (13)

Resolution:

Install Nmap for windows :

https://nmap.org/download.html#windows

>>alias nmap='"/mnt/c/Program Files (x86)/Nmap/nmap.exe"