[systemd] Increase StartLimitBurst from 2 to 3

It might be that 2 is too small because also manual restarts
are counted to failed service. Let's increase value by one so
that we don't get any problems during system update.

Signed-off-by: Matti Kosola <matti.kosola@jollamobile.com>
Merge pull request #69 from mkosola/master

Increase StartLimitBurst from 2 to 3