inet: Fix threaded res_init

inet: Fix threaded res_init

In a multi-threaded application where res_init() was called either
directly or implicitly, getaddrinfo() and others failed to add the
DNS search domain to hostnames.

This problem made it not possible to look up a hostname without its
domain appended.

The problem is caused by res_sync_func() overwriting the configuration
read by __open_nameservers() immediately after it is read.

The suggested solutin is to disable res_sync_func() while reading name
server configuration in res_init().

Signed-off-by: Kenneth Soerensen <kenneth.sorensen@spectralink.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>