Fix source address IPHC
add mutex_unlock_and_sleep()
add test for mutex_unlock_and_sleep()
posix: Disable debug output of pthreads

`DEBUG_ENABLED` should be enabled during debugging, and disabled
afterwards.
Fix `pthread_mutex_lock()` check in test_pthread_cooperation
Merge pull request #728 from BytesGalore/add_unlock_mutex_and_sleep

core:mutex: enable atomic execution of unlock a mutex and sleep for a thread
Merge pull request #849 from Kijewski/issue-844

posix: Fix `pthread_mutex_lock()` check in test_pthread_cooperation
Auto init source address mode
Fix test_net_if
Merge pull request #852 from authmillenon/autoinit-src-addr-mode

net_if/auto_init: Auto init source address mode
Merge pull request #843 from authmillenon/fix-lowpan-iphc

sixlowpan: Fix source address IPHC
Merge pull request #848 from Kijewski/that-annoying-debug-flag-in-pthread-that-effing-needs-to-go-away-already

posix: Disable debug output of pthreads
Merge pull request #853 from authmillenon/fix-test-net-if

tests: Fix test_net_if