sys/socket.h: add MSG_ZEROCOPY from linux v4.14

MSG_ZEROCOPY socket send flag avoids copy in the kernel
new in linux commit 52267790ef52d7513879238ca9fac22c1733e0e3
SO_ZEROCOPY socket option enables MSG_ZEROCOPY if availale
new in linux commit 76851d1212c11365362525e1e2c0a18c97478e6b

include/sys/socket.h

@@ -232,6 +232,7 @@ struct linger {
 #define SO_COOKIE               57
 #define SCM_TIMESTAMPING_PKTINFO 58
 #define SO_PEERGROUPS           59
+#define SO_ZEROCOPY             60
 
 #ifndef SOL_SOCKET
 #define SOL_SOCKET      1
@@ -285,6 +286,7 @@ struct linger {
 #define MSG_MORE      0x8000
 #define MSG_WAITFORONE 0x10000
 #define MSG_BATCH     0x40000
+#define MSG_ZEROCOPY  0x4000000
 #define MSG_FASTOPEN  0x20000000
 #define MSG_CMSG_CLOEXEC 0x40000000