tipc: use consistent GFP flags

Some functions, like tipc_crypto_start use inconsisten GFP flags
when allocating memory. The mentioned function use GFP_ATOMIC to
to alloc a crypto instance, and then calls alloc_ordered_workqueue()
which allocates memory with GFP_KERNEL. tipc_aead_init() function
even uses GFP_KERNEL and GFP_ATOMIC interchangeably.
No doc comment specifies what context a function is designed to
work in, but the flags should at least be consistent within a function.

Cc: Jon Maloy <jmaloy@redhat.com>
Cc: Ying Xue <ying.xue@windriver.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Cc: tipc-discussion@lists.sourceforge.net
Cc: linux-kernel@vger.kernel.org

Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>