USB: gadget: u_ether: Change skb->len check for jumbo frames

There is a chance that jumbo frames whose length greater than
EHT_FRAME_LEN(1514) can be sent by host if it is configured for MTU sizes
greater than 1500. Currently driver is checking for skb->len greater than
ETH_FRAME_LEN, which fails in case of jumbo frames received. Hence fix the
issue by changing check for skb->len > GETHER_MAX_ETH_FRAME_LEN in rx_work.

Change-Id: I4b09419d026a16563e03b891fe671e748f911dad
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>