After resetting iOS 7, and having my volume disappear, how can I re-enable it? I just did a hard reset on my iPhone 4S by wiping the phone and restoring an iCloud backup. During that process, I used my iPad charger to make sure it stayed charged while it was being wiped and restored. 

However, after the restore was complete and my phone was back up and running the volume control was gone. It was simply non-existent in Control Center, grayed out in Music.app, and the volume buttons didn't work. It looked like what happens when the phone is connected to a car stereo, for example. Interestingly, the ringer control in Settings -> Sounds, worked.

I have tried: 


Rebooting the device
Playing music, and a video (which work through headphones, but not the speakers)
Tested Siri to confirm that it wasn't a hardware problem in the speakers actually malfunctioning.
Closed all apps, except one. 
Tried testing sounds with an alarm app, which didn't play as well.


Any ideas on how I can fix this?
To fix this problem, I got my iPad charger (which was disconnected from any power source such as a wall outlet), and plugged it into my iPhone, and unplugged it twice. This process fixed the iPhone.