Fix initdb's handling of min_wal_size and max_wal_size.

In commit 3e51b27, I misinterpreted the coding in setup_config()
as setting min_wal_size and max_wal_size to compile-time-constant
values.  But it's not: there's a hidden dependency on --wal-segsize.
Therefore leaving these variables commented out is the wrong thing.
Per report from Andres Freund.

Discussion: https://postgr.es/m/20230322200751.jvfvsuuhd3hgm6vv@awork3.anarazel.de

Author: tglsfdc

src/bin/initdb/initdb.c

@@ -1279,6 +1279,13 @@ setup_config(void)
 	conflines = replace_guc_value(conflines, "dynamic_shared_memory_type",
 								  dynamic_shared_memory_type, false);
 
+	/* Caution: these depend on wal_segment_size_mb, they're not constants */
+	conflines = replace_guc_value(conflines, "min_wal_size",
+								  pretty_wal_size(DEFAULT_MIN_WAL_SEGS), false);
+
+	conflines = replace_guc_value(conflines, "max_wal_size",
+								  pretty_wal_size(DEFAULT_MAX_WAL_SEGS), false);
+
 	/*
 	 * Fix up various entries to match the true compile-time defaults.  Since
 	 * these are indeed defaults, keep the postgresql.conf lines commented.
@@ -1289,12 +1296,6 @@ setup_config(void)
 	conflines = replace_guc_value(conflines, "port",
 								  DEF_PGPORT_STR, true);
 
-	conflines = replace_guc_value(conflines, "min_wal_size",
-								  pretty_wal_size(DEFAULT_MIN_WAL_SEGS), true);
-
-	conflines = replace_guc_value(conflines, "max_wal_size",
-								  pretty_wal_size(DEFAULT_MAX_WAL_SEGS), true);
-
 #if DEFAULT_BACKEND_FLUSH_AFTER > 0
 	snprintf(repltok, sizeof(repltok), "%dkB",
 			 DEFAULT_BACKEND_FLUSH_AFTER * (BLCKSZ / 1024));