Merge net branch into master

Main changes:

- MQTT fixes
- echo-server and echo-client fixes in net samples
- Fix build errors in net when using ISSM's llvm/icx compiler

----------------------------------------------------------------
Flavio Santes (4):
      net/mqtt: Add support for QEMU x86
      net/mqtt: Use uint32_t for Remaining Length encoding/decoding
      net/mqtt: Add payload size validation
      net/mqtt: Remove length computations for some msg fields

Jorge Ramirez-Ortiz (1):
      net/mqtt: Add support for IBM BlueMix Watson topic format

Jukka Rissanen (3):
      samples: net: Remove obsolete prj_slip.conf from echo-*
      samples: net: Remove the README file
      samples: net: Add README.rst to echo apps

Tomasz Bursztyka (2):
      net: Fix a const specifier issue
      net: Remove duplicate const specifier

 include/net/mqtt_types.h                           |   4 +-
 include/net/net_if.h                               |   2 +-
 include/net/net_l2.h                               |   4 +-
 samples/net/README                                 |  89 ------------------
 samples/net/echo_client/README.rst                 |  98 ++++++++++++++++++++
 samples/net/echo_client/prj_slip.conf              |  26 ------
 samples/net/echo_server/README.rst                 | 102 +++++++++++++++++++++
 samples/net/mqtt_publisher/README.rst              |   6 ++
 .../prj_qemu_x86.conf}                             |  31 ++++---
 samples/net/mqtt_publisher/src/config.h            |   2 +
 samples/net/mqtt_publisher/src/main.c              |  58 ++++++++++--
 samples/net/mqtt_publisher/testcase.ini            |   2 +-
 subsys/net/lib/mqtt/mqtt_pkt.c                     |  27 +++---
 tests/net/lib/mqtt_packet/src/mqtt_packet.c        |  67 ++++++++++----
 14 files changed, 346 insertions(+), 172 deletions(-)
 delete mode 100644 samples/net/README
 create mode 100644 samples/net/echo_client/README.rst
 delete mode 100644 samples/net/echo_client/prj_slip.conf
 create mode 100644 samples/net/echo_server/README.rst
 rename samples/net/{echo_server/prj_slip.conf => mqtt_publisher/prj_qemu_x86.conf} (63%)

Change-Id: I56bf74032f37f4aa09046c036e8b0f22dd926c54
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>