net*: remove remnants of caddr_t

[glebius]

Summary

caddr_t is a typedef for a character pointer (char *) that originated in
Version 7 Unix, released by AT&T in 1979. It became obsolete in 1989,
when ANSI C introduced void *.

What's left:

• ioctl(9) KPI still uses caddr_t, thus network related ioctl method still use it.
• if_clone KPI, to be done separately.
• bpf(4), to be done separately.
• SCTP, let maintainers decide.
• iflib(4), let maintainers decide.

[zlei]

Generally looks good to me.

sys/netinet/ip_input.c

1020

No need to cast to char *.

sys/netinet/tcp_output.c

2101

sys/netinet/tcp_stacks/rack.c

18121

sys/netinet/tcp_subr.c

1799

1799

Given m is a new allocated mbuf, I believe that ip6 will not overlap with the mbuf data. So we can safely use memcpy() other than bcopy().

Let transport decide.

1812

1846

1860

sys/netinet6/icmp6.c

1423

We can use memcpy here.

sys/netinet6/ip6_input.c

1032

Can safely use memcpy.

sys/netinet6/ip6_output.c

3194

Can safely use memcpy.

[glebius]

There are many places where memcpy() can be used. I don't want to mix that into this commit.

[glebius]

Commited d7cf2e714e29a52264fa4bc67e7d727948003afb