imtcp: fix busy-loop in the tcp listener

This patch fixes the high CPU usage when rsyslog
run out of FDs

reference
http://lists.adiscon.net/pipermail/rsyslog/2013-October/034488.html

Signed-off-by: Mohit Agrawal <moagrawa@redhat.com>
Signed-off-by: Susant Sahani <susant@redhat.com>
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