Fix some clang warnings when using PubNub through cocoa pods

Looks like the private macro file generates a few warnings when using pub nub as a cocoa pod. I'm not sure why it happens, since these functions are actually used. I'm suspecting the header gets included multiple times and ends up not using all the functions.
I've marked them as inline, which seems reasonable since most are very short anyway.

Also, the unused kPNDefaultGrantPeriod apparently came back, even though a pull request fixed it with 3.5.5