[DOCS] Fix typo in link text
[DOCS] Fix typo in link text

The "Known Issue" link to IMPALA-1480 is the full
URL + the text "IMPALA-1480" after it, instead of
"IMPALA-1480" being the link, because "IMPALA-1480"
went by accident outside the </xref> end tag for
the link.

Also fill in Known Issues title for IMPALA-3441.

Change-Id: I87b6c7b9f4c6db50c63aed7f6248dc8e808e4f6f
Reviewed-on: http://gerrit.cloudera.org:8080/5881
Reviewed-by: Jim Apple <396f577ccd0f19e47f0fb44dae1d6fc43cc20400@apache.org>
Tested-by: Impala Public Jenkins

cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala