daemon.c: Fix variable overflow.
daemon.c: Fix variable overflow.

The mmap's length argument should be of type "size_t".
Before this fix, the implementation has the risk of
overflow since the length is calculated by the
multiply of two "unsigned int".

Signed-off-by: Alex Wang <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@awakenetworks.com>

google/testimony,awakenetworks/testimony,google/testimony,awakenetworks/testimony,awakenetworks/testimony,google/testimony