Remove duplicate initialization of field in nscd.

I'm looking at the warnings from building glibc with -Wextra, to see
if we could use -Wextra by default, possibly with a few of its
warnings disabled, and so benefit from warnings in -Wextra but not in
-Wall.  (The vast bulk of the extra warnings so produced are from
-Wunused-parameter -Wsign-compare -Wmissing-field-initializers
-Wtype-limits, so I expect those would be disabled at least at first.)

Various miscellaneous warnings show up with -Wextra that it clearly
seems to make sense to fix independent of whether we add -Wextra to
the normal options for building glibc.  This patch fixes one:
"initialized field overwritten [-Woverride-init]" in nscd.

Tested for x86_64.

	* nscd/connections.c (reqinfo): Initialize SHUTDOWN element only
	once.