Commit 
107db7ec7838 ("docs: networking: convert 6lowpan.txt to ReST")
renamed 6lowpan.txt to 6lowpan.rst for the ReST conversion.
Since then, ./scripts/get_maintainer.pl --self-test complains:
  warning: no file matches F: Documentation/networking/6lowpan.txt
Adjust 6LOWPAN GENERIC (BTLE/IEEE 802.15.4) entry in MAINTAINERS.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
 S:     Maintained
 F:     net/6lowpan/
 F:     include/net/6lowpan.h
-F:     Documentation/networking/6lowpan.txt
+F:     Documentation/networking/6lowpan.rst
 
 6PACK NETWORK DRIVER FOR AX.25
 M:     Andreas Koensgen <ajk@comnets.uni-bremen.de>