tests: fixed multiple tests not properly waiting for packets to be re…

…ceived

- dhcpv4 : 1 HV, 2 LS, 2 LSPs/LS
- dns lookup : 1 HV, 2 LS, 2 LSPs/LS
- dhcpv6 : 1 HV, 2 LS, 5 LSPs
- IPv6 ND Router Solicitation responder
- 4 HV, 1 LS, 1 LR, packet test with HA distributed router gateway port
- send gratuitous arp for NAT rules on distributed router
- send gratuitous ARP for NAT rules on HA distributed router
- external logical port

Some of those tests were already "waiting" for packets but were either waiting
for the expected number of packets (and hence failing if a garp was received),
or were waiting just for a few more packets, to handle garp (but were failing
if more garp were received, and were slower than expected as always waiting for
a few additional packets).

Signed-off-by: Xavier Simonart <xsimonar@redhat.com>
Signed-off-by: 0-day Robot <robot@bytheb.org>