BUG/MINOR: check: Wake the check task if the check is finished in wake_srv_chk()

BUG/MINOR: check: Wake the check task if the check is finished in wake_srv_chk()

With tcp-check, the result of the check is set by the function tcpcheck_main()
from the I/O layer. So it is important to wake up the check task to handle the
result and finish the check. Otherwise, we will wait the task timeout to handle
the result of a tcp-check, delaying the next check by as much.

This patch also fixes a problem about email alerts reported by PiBa-NL (Pieter)
on the ML [1] on all versions since the 1.6. So this patch must be backported
from 1.9 to 1.6.

[1] https://www.mail-archive.com/haproxy@formilux.org/msg32190.html