mlx5_core: fix deadlock when using RXTLS

If removing a node of type FS_TYPE_FLOW_DEST we lock the flow group too
late. This can lead to a deadlock with fs_add_dst_fg().

PR: 274715
Reviewed by: kib
Tested by: mm
Differential Revision: https://reviews.freebsd.org/D42368

(cherry picked from commit a592812327deaf69ab226afc5c8a01af43dc03c2)