Merge remote-tracking branch 'cros/upstream' into merge-upstream

26ec43c sar: add support for Transmission Status
e9b5af3 sar: add missing Since tags in enums
9cb417b mbimcli,sar: reword command help items
d3ed5f9 mbimcli,sar: set operations receive strings, not flags
701de6d libmbim-glib,sar: renamed Transmission Status related enums
6a0fd38 docs: add missing doc for Transmission Status related enums
97028c6 mbim-codegen: avoid struct plurals in method documentation
55aca95 doc: skip running gtkdoc-rebase on local install step
fdd51e5 docs: add 'online-location' reference
e2b3546 core: update copyright years to 2021
2731324 build: add new RELEASING doc explaining how releases are made
76c8be6 README: add CoC info

BUG=None
TEST=deploy MM and libmbim to jinlon and test internet connection

Change-Id: I1d91abbda739c5db0ae32690040095965cafa2a2