Add _POSIX_C_SOURCE for getline and fix function prototypes

Author: ayushman1210

src/sipnet/events.c

@@ -10,6 +10,8 @@
  */
 // clang-format on
 
+#define _POSIX_C_SOURCE 200809L
+
 #include "events.h"
 #include <math.h>
 #include <stdio.h>