destiny: wireshark compliant tcp flags
This enum is also used to set the tcp flags within a tcp header.
With the current values in this enum, wireshark is not able to
recognize the tcp segments as their actual tcp type,
and thus odd messages in wireshark appear.

destiny: reusing tcp flags for combinations
core/cortex-m: add missing NORETURNs to thread_arch
destiny: change byte order of ipv6_header->length
When accessing the length field of an ipv6_header a byte order switch (host -> network) is necessary.
Otherwise, it breaks calculations or the checksum and other tcp related computations.
Furthermore, when writing to ipv6_header->length it is important to switch this
from host byte order to network byte order.
Merge pull request #1275 from cgundogan/fix_tcp_flags_for_wireshark

destiny: wireshark compliant tcp flags
Merge pull request #1300 from cgundogan/fix_wrong_byte_order_ipv6_length

destiny: change byte order of ipv6_header->length
Merge pull request #1292 from Kijewski/issue-1288

core/cortex-m: add missing NORETURNs to thread_arch
core/include/arch/irq_arch.h: fix typo and trailing whitespaces
Merge pull request #1308 from N8Fear/fix-typo-and-whitespaces

core/include/arch/irq_arch.h: fix typo and trailing whitespaces
core/msg: prevent null pointer dereference
core/msg: reenable interrupts in msg_snd_int
SQASHME s/printf/DEBUG/
SQASHME add `DEBUG` msg to `msg_send`, too
core/msg_send: fix target check race condition

Move `dINT` up and add corresponding `eINT`.

Fixes a race condition in case of a context switch after check for
`target != NULL` which leads to the thread exiting.
SQASHME: core/msg: call dINT even earlier in msg_send

.. and accompany by eINT which is required now

Addresses https://github.com/RIOT-OS/RIOT/pull/1285#discussion-diff-13593644
SQASHME: fix c&p error in debug message