This patch prevents (i guess) races when kernel code works with an address lists.

For example, it should resolve this problem:
http://lists.freebsd.org/pipermail/freebsd-current/2007-June/073348.html

Changes:
	o Access to the in_ifaddrhashtbl protected with the rwlock;
	o Access to the in_ifaddrhead protected with the rwlock;
	o Several style(9) fixes;
	o Removed NULL-pointer check after M_WAITOK malloc;
	o Replaced several for(...) to TAILQ_FOREACH;

(c) Andrey V. Elsukov <bu7cher (at) yandex.ru>