iptables: move manpage

Rename libipt_{time,u32}.man to libxt_{time,u32}.man to go
in line with the C files.

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>

diff --git a/extensions/libipt_time.man b/extensions/libxt_time.man
similarity index 100%
rename from extensions/libipt_time.man
rename to extensions/libxt_time.man

diff --git a/extensions/libipt_u32.man b/extensions/libxt_u32.man
similarity index 100%
rename from extensions/libipt_u32.man
rename to extensions/libxt_u32.man