tests: fix mutex_unlock_and_sleep pids
Merge pull request #1744 from N8Fear/fix-mutex_unlock_and_sleep

tests: fix mutex_unlock_and_sleep pids
sixlowpan: fixed net_if counter

This is a fixup for 11254577eb01178b4ca90fe6383987cc0721fca6 which
caused this function to always return a positive number, when any
interfaces was configured.
drivers/periph/gpio: increase possible gpio number
Merge pull request #1748 from LudwigOrtmann/raisingthebar

drivers/periph/gpio: increase possible gpio number
Merge pull request #1745 from OlegHahm/is_our_address_fixup

sixlowpan: fixed net_if counter