streamline_config.pl: add softtabstop=4 for vim users

The tab stop for Perl files is by default (at least in emacs) to be 4
spaces, where a tab is used for all 8 spaces.  Add a local variable
comment to make vim do the same by default, and this will help keep the
file consistent in the future when others edit it via vim and not emacs.

Link: https://lkml.kernel.org/r/20210322214032.293992979@goodmis.org


Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: "John (Warthog9) Hawley" <warthog9@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>