Revert "keepalived: needs headers >= 3.4"

This reverts commit d01b0bba.

Original commit  made restriction for Linux headers < 3.4 which was
related to keepalived version 1.3.5, but it compiles fine now at least
with a toolchain based on 3.2 headers and keepalived 2.0.15 together
with ipset enabled.

Probably it was fixed by this commit:

    https://github.com/acassen/keepalived/commit/5a7f895bb795269f79e6353c6269dfbc0b782281



Signed-off-by: Vadym Kochan <vadym.kochan@plvision.eu>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>