tipc: Relocate trivial link status functions to header file

Rather than live in link.c where they can only be used in that file alone,
these helper routines are better served by being in link.h

Relocated are the following:

	link_working_working
	link_working_unknown
	link_reset_unknown
	link_reset_reset
	link_blocked
	link_congested

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>