User preference for maxSimultaneousUpload

Consider the user preferences for maximum number of simultaneous uploads.
The user can select a value only lower than that set by the server-side
config.

Since the user set value is smaller than the server-side config the JS
only checks for the user setting.

Bug: 39607
Change-Id: I30cc9c0629c0d38a72bd04000b04579686f4f920
Merge "User preference for maxSimultaneousUpload"