PX4/NuttX branch test: master

NuttX:
 - https://github.com/PX4-NuttX/nuttx/tree/master
 - PX4/NuttX@7815c3a

Changes from PX4/NuttX (PX4/NuttX@423371c) in current PX4/master (fecb32f)
PX4/NuttX@423371c...7815c3a

7815c3a (HEAD, origin/master) Merged in masayuki2009/nuttx.nuttx/tiva_with_qemu (pull request #927)
b6e7812 Merged in masayuki2009/nuttx.nuttx/fix_gs2200m (pull request #926)
1346f29 net/: Fix alignment and spacing problems found by tools/nxstyle.
7b554d6 Update README
79e79f0 Merged in alinjerpelea/nuttx (pull request #925)
574595d Still fixing new warnings found in build testing.
8774977 Fix warnings found in build testing.
077d164 /net/inet: Simplify design of change in last commit.
de5a616 This commit implements a proper version of SO_LINGER.  Not sufficiently tested on initial commit.
ded1900 include/nuttx/net/net.h:  Fix some long lines.

Apps:
 - https://github.com/PX4/NuttX-apps/tree/master
 - PX4/NuttX-apps@ee8af2a

Changes from PX4/NuttX-apps (PX4/NuttX-apps@7db2a35) in current PX4/master (fecb32f)
PX4/NuttX-apps@7db2a35...ee8af2a

ee8af2a (HEAD -> master, origin/master) Fix warnings found in build testing.
334b450 wireless/gs2200m/gs2200m_main.c:  Fix a warning about an uninitialized return value found in build testing.
18a8032 examples/vl53l1x:  Remove.  The driver does not compile.
94ac7dc examples/vl53l1x:  Add VL53L1X example demo.
27766d7 Merged in masayuki2009/nuttx.apps/fix_apps_industry (pull request #178)
d2f3ad9 Merged in masayuki2009/nuttx.apps/wireless_gs2200m (pull request #177)
2c8e349 Merged in masayuki2009/nuttx.apps/add_system_gs2200m (pull request #176)
6561573 industry/abnt_codi, include/industry/abnt_code.h, examples.abntcodi:  Adds support for ABNT CODI library.  This is an energy meter protocol used in Brazil.
bd14bf7 apps/netutils/json:  Removed.  Replaced with apps/netutils/cjson.
24e590b apps/nshlib/nsh_ddcmd.c:  Seemingly nonsense change but somehow works around a compilation error using the ZDS-II toolchain.  It was claiming that vtbl was undefined indd_outfopen().