icmp: account for ICMP out errors because of socket limit

[zhuyj]

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Hi, Eric && David

 ____           ______________
|    |         |              |
| PC |<------->| MIPS 32 core |
|____|         |______________|

When ping from a PC to a board (MIPS 32 core), because of socket limit,
ping echo will fail. But ICMP_MIB_OUTERRORS counter is not incremented.
In this case, "netstat -s" can not report these errors.

This patch will fix this problem. Now it is in the attachment. Please 
check it.

Best Regards!
Zhu Yanjun