[connman] Increase maximum size of stats files.

The default maximum size of the stats files was 16 kB. However, now
that each record is approximately twice as big (due to the change from
32 bit to 64 bit data types) the number of records which can be stored
has halved. To compensate increase the default maximum size to 32 kB.
[connman] Fix erroneous data counters when roaming.

The home and roaming pointers in the stats file header are not updated
when summarising the history file. This can result in the home or
roaming pointer pointing to an invalid record. Fixed by setting both
values to UINT_MAX (invalid) when the history file is updated.
[connman] check service ID validity

storage: check service ID validity

Connman service ID is used, in the form it is read from storage, as
part of D-Bus path in connmand's D-Bus API. If the path constructed
using the service ID does not conform to D-Bus specifications, D-Bus
library assertion will cause connmand to exit; on restart the same
invalid ID is read from the storage and the assertion is triggered
again.

I experienced a connmand restart loop because some apparently
wispr-related memory corruption caused a service ID with binary
characters to be stored on disk. While that bug should be fixed also,
sanity-checking the service ID does not harm.
Merge pull request #76 from amccarthy/master

Data counter fixes
Merge pull request #80 from lpotter/master

[connman] fix scan when no networks.
Merge pull request #77 from hmallat/sanity-check-service-id

[connman] check service ID validity
[connman] loosen the autoconnect failure clamp.

This fixes the condition when on the edge of a low signal, the
autoconnect keeps attempting to connect, Whereas before it would try
once, and then be locked out, until user manually connected.