Fix typo in overlay log message

[thaJeztah]

fixes docker/for-linux#89

thanks @alainvanhoof for reporting

ping @abhi PTAL

[abhi]

LGTM :)

[codecov-io]

Codecov Report

Merging #1973 into master will decrease coverage by 0.51%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1973      +/-   ##
==========================================
- Coverage    38.5%   37.98%   -0.52%     
==========================================
  Files         137      137              
  Lines       27351    27351              
==========================================
- Hits        10531    10389     -142     
- Misses      15523    15690     +167     
+ Partials     1297     1272      -25

Impacted Files	Coverage Δ
drivers/overlay/ov_network.go	0.26% <0%> (ø)	⬆️
networkdb/networkdb.pb.go	37.31% <0%> (-5.17%)	⬇️
networkdb/delegate.go	70.07% <0%> (-4.61%)	⬇️
endpoint_cnt.go	83.47% <0%> (-2.61%)	⬇️
cmd/proxy/tcp_proxy.go	80.76% <0%> (-1.93%)	⬇️
networkdb/cluster.go	46.3% <0%> (-1.6%)	⬇️
iptables/iptables.go	53.71% <0%> (-0.86%)	⬇️

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[fcrisciani]

Lgtm