BACKPORT: FROMGIT: binder: pre-allocate binder_transaction

Move the allocation of 'struct binder_transaction' to the beginning of
the binder_transaction() function, along with the initialization of all
the members that are known at that time. This minor refactoring helps to
consolidate the usage of transaction information at later points.

This patch is in preparation for binder's generic netlink implementation
and no functional changes are intended.

Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20250727182932.2499194-2-cmllamas@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Bug: 372832477
(cherry picked from commit 4afc5bf0
 git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git

 char-misc-next)
[cmllamas: fix minor conflicts with t->priority]
Change-Id: I588319183f1d69e3694b00341432d6d4eee0a697
Signed-off-by: Carlos Llamas <cmllamas@google.com>