Kernel: Add MSG_PEEK support for the IPv4Socket

This commit will add MSG_PEEK support, which allows a package to be
seen without taking it from the buffer, so that a subsequent recv()
without the MSG_PEEK flag can pick it up.

Userland/Libraries/LibC/sys/socket.h

@@ -46,6 +46,7 @@ __BEGIN_DECLS
 
 #define MSG_TRUNC 0x1
 #define MSG_CTRUNC 0x2
+#define MSG_PEEK 0x4
 #define MSG_DONTWAIT 0x40
 
 typedef uint16_t sa_family_t;