[CFR] correct type of addrinfo.ai_addrlen and netent.n_net

Hi,

The ai_addrlen of a struct addrinfo used to be a size_t, per RFC 2553.
In XNS5.2, and subsequently in POSIX-2001 and RFC 3493, it was changed
to a socklen_t.
And, the n_net of a struct netent used to be an unsigned long integer.
In XNS5, and subsequently in POSIX-2001, it was changed to an
uint32_t.

I made a patch to correct these:

    http://www.imasy.or.jp/~ume/FreeBSD/netdb.h-padding.diff

To accomodate for this while preserving ABI compatibility with the old
interface, we need to prepend or append 32 bits of padding, depending
on the (LP64) architecture's endianness.  I wish to delete these
padding before 6.0-RELEASE.

Please review it.

Sincerely,

--
Hajimu UMEMOTO _at_ Internet Mutual Aid Society Yokohama, Japan
ume_at_mahoroba.org  ume_at_{,jp.}FreeBSD.org
http://www.imasy.org/~ume/