unic: export the function of getting l3_type for UB

driver inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I850RQ


CVE: NA

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When the driver runs in UB mode, parsing l3 type of the packet depends
on the ptype table which located in hns3_enet marked as static.

This patch exports the function of getting l3_type for parsing
L3 type in UNIC RX.

Signed-off-by: Fengyan Mu <mufengyan@hisilicon.com>
Signed-off-by: Junxin Chen <chenjunxin1@huawei.com>