ddb: use 'textdump dump' instead of 'call doadump'

The change is for the example in textdump.4 and the default ddb.conf.

First of all, doadump now requires an argument and it won't do a
textdump if the argument is not 'true'.
And 'textdump dump' is more idiomatic anyway.

For what it's worth, ddb 'dump' command seems to always request a vmcore
dump even if a textdump was requested earlier, e.g., by 'textdump set'.
Finally, ddb 'call' command is not documented.

MFC after:	2 weeks

sbin/ddb/ddb.conf

@@ -9,7 +9,7 @@
 script lockinfo=show locks; show alllocks; show lockedvnods
 
 # kdb.enter.panic	panic(9) was called.
-script kdb.enter.panic=textdump set; capture on; run lockinfo; show pcpu; bt; ps; alltrace; capture off; call doadump; reset
+script kdb.enter.panic=textdump set; capture on; run lockinfo; show pcpu; bt; ps; alltrace; capture off; textdump dump; reset
 
 # kdb.enter.witness	witness(4) detected a locking error.
 script kdb.enter.witness=run lockinfo

share/man/man4/textdump.4

@@ -27,7 +27,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 30, 2018
+.Dd October 18, 2019
 .Dt TEXTDUMP 4
 .Os
 .Sh NAME
@@ -162,7 +162,7 @@ invoke panic in order to force a kernel dump to be written out followed by a
 reboot:
 .Bd -literal -offset indent
 script kdb.enter.panic=textdump set; capture on; show allpcpu; bt;
-  ps; alltrace; show alllocks; call doadump; reset
+  ps; alltrace; show alllocks; textdump dump; reset
 .Ed
 .Pp
 In the following example, the script