Fix flaky frag6 19 test

[jlduran]

kyua test -k /usr/tests/Kyuafile sys/netinet6/frag6
sys/netinet6/frag6/frag6_01:frag6_01  ->  skipped: Sending IPv6 Jumbograms needs 1 kernel changes and BPF fixes  [0.013s]
sys/netinet6/frag6/frag6_02:frag6_02  ->  passed  [2.563s]
sys/netinet6/frag6/frag6_03:frag6_03  ->  passed  [2.438s]
sys/netinet6/frag6/frag6_04:frag6_04  ->  passed  [2.550s]
sys/netinet6/frag6/frag6_05:frag6_05_0  ->  failed: Global UDP statistics do not match: 6 != 9  [6.196s]
sys/netinet6/frag6/frag6_05:frag6_05_1  ->  failed: Global UDP statistics do not match: 6 != 9  [5.499s]
sys/netinet6/frag6/frag6_06:frag6_06_0  ->  passed  [3.027s]
sys/netinet6/frag6/frag6_07:frag6_07  ->  failed: Global UDP statistics do not match: 6 != 9  [6.470s]
sys/netinet6/frag6/frag6_08:frag6_08  ->  failed: Global UDP statistics do not match: 6 != 9  [6.802s]
sys/netinet6/frag6/frag6_09:frag6_09  ->  failed: Global UDP statistics do not match: 6 != 9  [5.673s]
sys/netinet6/frag6/frag6_10:frag6_10  ->  failed: Global UDP statistics do not match: 6 != 9  [5.698s]
sys/netinet6/frag6/frag6_11:frag6_11  ->  failed: Global UDP statistics do not match: 6 != 9  [5.257s]
sys/netinet6/frag6/frag6_12:frag6_12  ->  failed: Global UDP statistics do not match: 6 != 9  [5.577s]
sys/netinet6/frag6/frag6_13:frag6_13  ->  failed: Global UDP statistics do not match: 6 != 9  [5.312s]
sys/netinet6/frag6/frag6_14:frag6_14  ->  passed  [5.420s]
sys/netinet6/frag6/frag6_15:frag6_15  ->  passed  [2.599s]
sys/netinet6/frag6/frag6_16:frag6_16  ->  passed  [2.777s]
sys/netinet6/frag6/frag6_17:frag6_17  ->  passed  [4.004s]
sys/netinet6/frag6/frag6_18:frag6_18  ->  passed  [3.876s]
sys/netinet6/frag6/frag6_19:frag6_19  ->  failed: Global UDP statistics do not match: 6 != 9  [4.244s]
sys/netinet6/frag6/frag6_20:frag6_20  ->  passed  [5.390s]

Results file id is usr_tests.20231029-091047-402793
Results saved to /.kyua/store/results.usr_tests.20231029-091047-402793.db

11/21 passed (10 failed)