[net_util] fix comment on maximum PID in 18-bit space
[net_util] fix comment on maximum PID in 18-bit space

This changelist does not contain any functional modifications.

Change-Id: Ic3226c1b8c928e1558c9e62b7e43c80bdd8745e9
Reviewed-on: http://gerrit.cloudera.org:8080/13859
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Tested-by: Alexey Serbin <864f6b82bd94e8dda64141d4274519ee66e0102e@cloudera.com>

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