xfrm: esp: ipv4: fix up flags setting

xfrm: esp: ipv4: fix up flags setting

In commit ab8b995323e5 ("xfrm: esp: avoid in-place decrypt on shared skb
frags") in the 5.15.y tree, the tx_flags variable was set, instead of
flags.  This was due to me backporting the 6.1.y version of Ben's
version of the backport and not realizing the variable needed to be
different, so this was my fault, not his.

Link: https://lore.kernel.org/r/1b941a1353791ddd6fd75fb8e68b377367d689ff.camel@oracle.com
Reported-by: Dominik Grzegorzek <dominik.grzegorzek@oracle.com>
Reported-by: Massimiliano Pellizzer <mpellizzer.dev@gmail.com>
Cc: Ben Hutchings <benh@debian.org>
Fixes: ab8b995323e5 ("xfrm: esp: avoid in-place decrypt on shared skb frags")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>