Kernel: Add the SO_BINDTODEVICE socket option

This patch adds a way for a socket to ask to be routed through a
specific interface.
Currently, this option only applies to sending, however, it should also
apply to receiving...somehow :^)

Libraries/LibC/sys/socket.h

@@ -80,6 +80,7 @@ struct ucred {
 #define SO_ERROR 4
 #define SO_PEERCRED 5
 #define SO_REUSEADDR 6
+#define SO_BINDTODEVICE 7
 
 int socket(int domain, int type, int protocol);
 int bind(int sockfd, const struct sockaddr* addr, socklen_t);