cn10k-ipsec: Fix compilation error when CONFIG_XFRM_OFFLOAD disabled

cn10k-ipsec: Fix compilation error when CONFIG_XFRM_OFFLOAD disabled

Define static branch variable "cn10k_ipsec_sa_enabled"
in "otx2_txrx.c". This fixes below compilation error
when CONFIG_XFRM_OFFLOAD is disabled.

 drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.o:(__jump_table+0x8): undefined reference to `cn10k_ipsec_sa_enabled'
 drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.o:(__jump_table+0x18): undefined reference to `cn10k_ipsec_sa_enabled'
 drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.o:(__jump_table+0x28): undefined reference to `cn10k_ipsec_sa_enabled'

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412110505.ZKDzGRMv-lkp@intel.com/
Fixes: 6a77a158848a ("cn10k-ipsec: Process outbound ipsec crypto offload")
Signed-off-by: Bharat Bhushan <bbhushan2@marvell.com>
Link: https://patch.msgid.link/20241211062419.2587111-1-bbhushan2@marvell.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>