Add struct sock_txtime and related flags

These are needed to use the SO_TXTIME socket option on Linux, which is
already exposed.

Author: ghedo

src/unix/linux_like/linux/mod.rs

@@ -563,6 +563,12 @@ s! {
         pub instruction_pointer: ::__u64,
         pub args: [::__u64; 6],
     }
+
+    // linux/net_tstamp.h
+    pub struct sock_txtime {
+        pub clockid: ::clockid_t,
+        pub flags: ::__u32,
+    }
 }
 
 s_no_extra_traits! {
@@ -2510,6 +2516,8 @@ pub const SOF_TIMESTAMPING_RX_SOFTWARE: ::c_uint = 1 << 3;
 pub const SOF_TIMESTAMPING_SOFTWARE: ::c_uint = 1 << 4;
 pub const SOF_TIMESTAMPING_SYS_HARDWARE: ::c_uint = 1 << 5;
 pub const SOF_TIMESTAMPING_RAW_HARDWARE: ::c_uint = 1 << 6;
+pub const SOF_TXTIME_DEADLINE_MODE: u32 = 1 << 0;
+pub const SOF_TXTIME_REPORT_ERRORS: u32 = 1 << 1;
 
 // linux/if_alg.h
 pub const ALG_SET_KEY: ::c_int = 1;