add SO_BPF_EXTENSIONS socket option

this was introduced to query BPF extension support with getsockopt
in linux 3.14, commit ea02f9411d9faa3553ed09ce0ec9f00ceae9885e

include/sys/socket.h

@@ -203,6 +203,7 @@ struct linger
 #define SO_SELECT_ERR_QUEUE     45
 #define SO_BUSY_POLL            46
 #define SO_MAX_PACING_RATE      47
+#define SO_BPF_EXTENSIONS       48
 
 #ifndef SOL_SOCKET
 #define SOL_SOCKET      1