ethdev: fix mtu comment
ethdev: fix mtu comment

In commit 59d0ecdbf0e1d6350 ("MTU accessors"),
max_frame_size was replaced with mtu.
Default size is ETHER_MTU = 1500.

Signed-off-by: Stephen Hemminger <06fa905d7f2aaced6dc72e9511c71a2a51e8aead@networkplumber.org>
Acked-by: Thomas Monjalon <ee2fa8b2681c737f775687e475dcbf2028a412f1@6wind.com>

phermansson/dpdk,phermansson/dpdk,phermansson/dpdk,phermansson/dpdk