core: introduce parse_ip_port (#4825)

1. Listed in TODO.
2. Tree wide replace safe_atou16 with parse_ip_port incase
   it's used for ports.

src/basic/parse-util.h

@@ -110,3 +110,5 @@ int parse_percent_unbounded(const char *p);
 int parse_percent(const char *p);
 
 int parse_nice(const char *p, int *ret);
+
+int parse_ip_port(const char *s, uint16_t *ret);