net: emaclite: fix handling for IP packets with specific lengths

The maximum length is capped similarly to the emaclite_send function.
Avoid integer underflow for values of ip->ip_len < 30, the minimum
length of an IP packet is 21 bytes.

Signed-off-by: Samuel Obuch <samuel.obuch@codasip.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Link: https://lore.kernel.org/r/20220927112103.155689-3-samuel.obuch@codasip.com


Signed-off-by: Michal Simek <michal.simek@amd.com>