fea: Handle funky input from netlink without crashing.

We found a situation where we were evidently getting a bad
subnet prefix (181) reported by netlink API.  This was causing
an un-caught exception that crashed FEA.

I think I found the right place to catch this exception, but
now I cannot reproduce the failure.  Leaving in a bit of debug
print statements in case this crops up again.

Signed-off-by: Ben Greear <greearb@candelatech.com>

xorp/fea/data_plane/control_socket/netlink_socket_utilities.cc

@@ -563,8 +563,18 @@ NlmUtils::nlm_get_to_fte_cfg(const IfTree& iftree, FteX& fte,
     //
     // TODO: define default admin distance instead of 0xffff
     //
-    fte = FteX(IPvXNet(dst_addr, dst_mask_len), nexthop_addr,
-	       if_name, vif_name, route_metric, 0xffff, xorp_route);
+    try {
+	fte = FteX(IPvXNet(dst_addr, dst_mask_len), nexthop_addr,
+		   if_name, vif_name, route_metric, 0xffff, xorp_route);
+    }
+    catch (XorpException& xe) {
+	err_msg += "exception in nlm_get_to_fte_cfg: ";
+	err_msg += xe.str();
+	err_msg += "\n";
+	XLOG_ERROR("exception in nlm_get_to_fte_cfg: %s", xe.str().c_str());
+	return XORP_ERROR;
+    }
+
     if (is_deleted)
 	fte.mark_deleted();
 

xorp/libxorp/exceptions.cc

@@ -134,6 +134,14 @@ InvalidNetmaskLength::InvalidNetmaskLength(const char* file,
     : XorpException("XorpInvalidNetmaskLength", file, line), 
       _netmask_length (netmask_length) 
 {
+    // There was a case where fea was crashing due to un-caught exception.
+    // Somehow, no useful info was being printed other than the exception
+    // name.  So, add some logging here just in case it happens again.
+    // (On reboot, couldn't cause the problem to happen again, so not sure
+    // I actually fixed the root cause in fea yet.)
+    cerr << "Creating InvalidNetmaskLength exception, file: "
+     << file << ":" << line << " netmask_length: " << netmask_length
+     << endl;
 } 
 
 const string