treewide: use uint* instead of u_int*

treewide: use uint* instead of u_int*

Gcc complains about missing types. Some commits introduced u_int* instead
of uint*. Use uint treewide.

Fixes errors in the form of:
In file included from xtables-legacy-multi.c:5:
xshared.h:83:56: error: unknown type name 'u_int16_t'; did you mean 'uint16_t'?
    83 | set_option(unsigned int *options, unsigned int option, u_int16_t *invflg,
        |                                                        ^~~~~~~~~
        |                                                        uint16_t
make[6]: *** [Makefile:712: xtables_legacy_multi-xtables-legacy-multi.o] Error 1

Avoid libipq API breakage by adjusting libipq.h include accordingly. For
arpt_mangle.h kernel uAPI header, apply same change as in kernel commit
e91ded8db5747 ("uapi: netfilter_arp: use __u8 instead of u_int8_t").

Signed-off-by: Nick Hainke <vincent@systemli.org>
Signed-off-by: Phil Sutter <phil@nwl.cc>