unic: Change the max frame size sent to firmware

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8LU51


CVE: NA

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Fix the problem that during driver initialization, the max
frame size sent to firmware is different from the value recorded
in driver in UB mode.
This patch change the max frame size configured in firmware
to 1500 from 1526.

Signed-off-by: Fengyan Mu <mufengyan@hisilicon.com>