svcgssd: check the return code from qword_eol() and log failures

svcgssd: check the return code from qword_eol() and log	failures

If qword_eol() fails while writing the context information, log
an indication of the failure.

This addresses at least one cause of the intermittent, and
previously undiagnosed, problem of the server returning
GSS_S_NO_CONTEXT when a context was seemingly successfully
created and sent down to the kernel.  In my case there was a
mis-match between kernel and user-land configuration resulting in
the proper kernel module not being loaded. Therefore the write
of the context failed, but was not logged by svcgssd.  When the
kernel goes to find the resulting context, it was really not
there and correctly returned GSS_S_NO_CONTEXT to the client.

Signed-off-by: Kevin Coffman <kwc@citi.umich.edu>
Signed-off-by: Steve Dickson <steved@redhat.com>