MINOR: resolvers: Add function to change the srv status based on SRV resolution

MINOR: resolvers: Add function to change the srv status based on SRV resolution

srvrq_update_srv_status() update the server status based on result of SRV
resolution. For now, it is only used from snr_update_srv_status() when
appropriate.

(cherry picked from commit 5efdef24c1753d7a68d1f6c8dc8cb6b4b84a3361)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 6d70368ab146925a9b2eae3963c5d92c00abe05d)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit d938bd528e3fa172f984cec4b8d7ae92dbb908a6)
[cf: Must be backported as far as 2.0 because of recent changes on resolvers]
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>