increment mode master lock timeout

merge request 4 contained a commit to increase the master lock timeout that was not picked. Still, for certain boards with higher quality VCXO's a lock timeout of 4 seconds is too short.

To my opinion there is no harm to increase this lock timeout since it doesn't slow down the normal lock process for other boards although a too tight timeout kicks in for boards that are slower.

Please reconsider since it is an essential commit for operating SPEC7 in "mode master".