Fix reads for sizes larger than INT_MAX in AF_INET lookup

Fix reads for sizes larger than INT_MAX in AF_INET lookup

Currently for AF_INET lookups from the hosts file, buffer sizes larger
than INT_MAX silently overflow and may result in access beyond bounds
of a buffer.  This happens when the number of results in an AF_INET
lookup in /etc/hosts are very large.

There are two aspects to the problem.  One problem is that the size
computed from the buffer size is stored into an int, which results in
overflow for large sizes.  Additionally, even if this size was
expanded, the function used to read content into the buffer (fgets)
accepts only int sizes.  As a result, the fix is to have a function
wrap around fgets that calls it multiple times with int sizes if
necessary.