sntp.h: document sntp_sync timeout unit
sntp.h: document sntp_sync timeout unit

It uses the same unit as sock_udp_recv.

authmillenon/RIOT,RIOT-OS/RIOT,BytesGalore/RIOT,kaspar030/RIOT,A-Paul/RIOT,x3ro/RIOT,LudwigKnuepfer/RIOT,aeneby/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,kbumsik/RIOT,cladmi/RIOT,ant9000/RIOT,LudwigOrtmann/RIOT,OlegHahm/RIOT,ant9000/RIOT,gebart/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,biboc/RIOT,aeneby/RIOT,yogo1212/RIOT,josephnoir/RIOT,kaspar030/RIOT,gebart/RIOT,miri64/RIOT,x3ro/RIOT,yogo1212/RIOT,OTAkeys/RIOT,toonst/RIOT,kaspar030/RIOT,basilfx/RIOT,ant9000/RIOT,mfrey/RIOT,josephnoir/RIOT,LudwigOrtmann/RIOT,miri64/RIOT,LudwigKnuepfer/RIOT,biboc/RIOT,yogo1212/RIOT,gebart/RIOT,basilfx/RIOT,biboc/RIOT,lazytech-org/RIOT,x3ro/RIOT,lazytech-org/RIOT,authmillenon/RIOT,LudwigOrtmann/RIOT,cladmi/RIOT,smlng/RIOT,toonst/RIOT,cladmi/RIOT,basilfx/RIOT,yogo1212/RIOT,neiljay/RIOT,A-Paul/RIOT,OTAkeys/RIOT,mtausig/RIOT,avmelnikoff/RIOT,aeneby/RIOT,gebart/RIOT,kYc0o/RIOT,neiljay/RIOT,kbumsik/RIOT,josephnoir/RIOT,authmillenon/RIOT,aeneby/RIOT,gebart/RIOT,neiljay/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,basilfx/RIOT,neiljay/RIOT,kaspar030/RIOT,lazytech-org/RIOT,OlegHahm/RIOT,toonst/RIOT,OTAkeys/RIOT,mfrey/RIOT,kbumsik/RIOT,avmelnikoff/RIOT,lazytech-org/RIOT,miri64/RIOT,OlegHahm/RIOT,LudwigKnuepfer/RIOT,avmelnikoff/RIOT,authmillenon/RIOT,avmelnikoff/RIOT,OTAkeys/RIOT,mfrey/RIOT,cladmi/RIOT,BytesGalore/RIOT,rfuentess/RIOT,mtausig/RIOT,mfrey/RIOT,kaspar030/RIOT,miri64/RIOT,aeneby/RIOT,miri64/RIOT,A-Paul/RIOT,kbumsik/RIOT,jasonatran/RIOT,basilfx/RIOT,A-Paul/RIOT,kYc0o/RIOT,BytesGalore/RIOT,BytesGalore/RIOT,jasonatran/RIOT,authmillenon/RIOT,OTAkeys/RIOT,rfuentess/RIOT,jasonatran/RIOT,A-Paul/RIOT,neiljay/RIOT,biboc/RIOT,josephnoir/RIOT,smlng/RIOT,ant9000/RIOT,smlng/RIOT,rfuentess/RIOT,LudwigOrtmann/RIOT,kYc0o/RIOT,x3ro/RIOT,cladmi/RIOT,toonst/RIOT,mtausig/RIOT,LudwigKnuepfer/RIOT,biboc/RIOT,mfrey/RIOT,kbumsik/RIOT,LudwigOrtmann/RIOT,smlng/RIOT,rfuentess/RIOT,mtausig/RIOT,smlng/RIOT,toonst/RIOT,yogo1212/RIOT,OlegHahm/RIOT,BytesGalore/RIOT,LudwigKnuepfer/RIOT,rfuentess/RIOT,yogo1212/RIOT,OlegHahm/RIOT,x3ro/RIOT,mtausig/RIOT,ant9000/RIOT,kYc0o/RIOT,avmelnikoff/RIOT,jasonatran/RIOT,LudwigOrtmann/RIOT,lazytech-org/RIOT