Switch to posix-socket

Switch to posix-socket

This commit replaces the old socket interface provided by lwip with a
driver that plugs into posix-socket. This removes the system call
definitions from lwip and separates system calls from the network
stack.

Signed-off-by: Marc Rittinghaus <marc.rittinghaus@kit.edu>
Reviewed-by: Cezar Craciunoiu <cezar.craciunoiu@gmail.com>
Reviewed-by: Razvan Deaconescu <razvan.deaconescu@cs.pub.ro>
Approved-by: Razvan Deaconescu <razvan.deaconescu@cs.pub.ro>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Pull-Request: #17