[ECOS] SNMP re-inits when session closed or trapsink removed -- FIX

[Tad <ecos_removethispart@ds3switch.com>]

If an SNMP session is closed or a trapsink is removed (which closes a 
session), the main select loop of snmpd will fail and re-init SNMP.

The cause appears to be outstanding select which returne EBADF = bad 
file descriptor(pointer?) for the socket that was closed out from under it.

Didn't know where this should be posted for the net-snmp guys, esp, 
cause I don't know if it affects their tree.  They don't have this fix 
as below in their latest.  Any suggestions on this question?

The simple fix appears to be to simply continue as if nothing happened, 
but it's possible that snmp_select_info() never should have added the 
closing socket to fdset in the first place.  It was getting very hard 
for me to determine whether the select was already outstanding when the 
socket closed or whether someone didn't set a proper "closing" flag that 
snmp_select_info() would recognize.  I tried updating  the 
snmp_select_info() to rev 1.245 of the 4.2 net-snmp tree which looks at 
closing sessions, but that didn't seem to help.

Here's the quick fix.  Most people probably don't close trapsinks too 
often and perhaps didn't even notice snmp re-init when they did.

snmpd.c : receive()
...
    count = select(numfds, &fdset, 0, 0, tvp);

    if (count > 0){
        snmp_read(&fdset);
    } else switch(count){
        case 0:
                snmp_timeout();
                break;
        case -1:
-        if (errno == EINTR){
+        if (errno == EINTR || errno == EBADF){
            continue;
        } else {
                    snmp_log_perror("select");
        }


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