Merge net branch into master

Main changes:

- DHCPv4 fixes
- Removing duplicate code in TCP
- Using proper net_buf APIs which helps debugging

----------------------------------------------------------------
Gil Pitney (1):
      net: offload_ip: Update net_context_accept_cb_t to net_tcp_accept_cb_t

Marcus Shawcroft (9):
      samples/mbedtls_dtls_client: Use k_uptime_get_32()
      samples/mbedtls_dtls_server: Use k_uptime_get_32()
      samples/mbedtls_dtls_client: Fix wild write in entropy_source
      samples/dhcpv4_client: Reduce default debug to dhcpv4
      samples/dhcpv4_client: Increase number of DATA buffers.
      samples/dhcpv4_client: Switch from private net_sprint_ipv4_addr to public net_addr_ntop
      net/dhcpv4: Add further diagnostics.
      net/dhcpv4: Use unique XID on each request.
      net/dhcpv4: Correct backoff and retransmit behaviour

Ravi kumar Veeramally (6):
      net: Ref net_buf using net_nbuf_ref
      net: tcp: Remove multiple checks on nbuf protocol family
      net: tcp: Remove multiple times of nbuf_compact() call
      net: samples: Unref net_buf using net_nbuf_unref
      net: tests: Unref net_buf using net_nbuf_unref
      net: samples: Unref the buf if app data length is zero

 include/net/dhcpv4.h                             |   6 +-
 include/net/offload_ip.h                         |   4 +-
 samples/net/dhcpv4_client/prj_frdm_k64f.conf     |  14 +--
 samples/net/dhcpv4_client/src/main.c             |  16 ++-
 samples/net/echo_client/src/echo-client.c        |   7 +-
 samples/net/echo_server/src/echo-server.c        |   2 +-
 samples/net/irc_bot/src/irc-bot.c                |   4 +-
 samples/net/leds_demo/src/leds-demo.c            |   4 +-
 samples/net/mbedtls_dtlsclient/src/dtls_client.c |  20 +--
 samples/net/mbedtls_dtlsserver/src/dtls_server.c |   5 +-
 samples/net/zoap_client/src/zoap-client.c        |   2 +-
 samples/net/zoap_server/src/zoap-server.c        |   4 +-
 samples/net/zperf/src/zperf_udp_receiver.c       |   2 +-
 subsys/net/ip/dhcpv4.c                           | 153 +++++++++++++++++++----
 subsys/net/ip/l2/arp.c                           |   2 +-
 subsys/net/ip/l2/bluetooth.c                     |   2 +-
 subsys/net/ip/l2/ieee802154/ieee802154_mgmt.c    |   2 +-
 subsys/net/ip/tcp.c                              |  28 ++---
 tests/net/ieee802154/l2/src/ieee802154_test.c    |   6 +-
 19 files changed, 187 insertions(+), 96 deletions(-)

Change-Id: Ic112cae20ad41bb76a85c8e1375a5cf533fa8278
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>