octeontx2-af: Fix uninitialized variable warning

Initialize l4_key_offset variable to fix uninitialized
variable compiler warning.

Fixes: b9b7421a ("octeontx2-af: Support ESP/AH RSS hashing")
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>