Add support to pad Ethernet frames to a minimum size

[shurd]

Summary

Some bnxt devices do not correctly send frames smaller than
52 bytes (without CRC), so add a quirk that will pad frames to an
arbitrary size before passing off to the encap routine.

Test Plan

Have Broadcom test with their broken hardware

[shurd]

Move BNXT_MIN_FRAME_SIZE into bnxt.h where D13269 defined BNXT_MIN_PKT_SIZE

[bhargava.marreddy_broadcom.com]

Thanks to Stephen,
Tested with Cumulus A0 NIC, test passed with this patch.
I'll delete the old workaround (used for padding) from driver.

[shurd]

Return an error of m_append() fails, not success.

[shurd]

Move ether padding into spearate function, predict_false() the length test

[shurd]

Mark iflib_ether_pad() as noinline and move device_printf() into it

[shurd]

Committed as r326578 (which had the wrong Differential Revision of D13269 specified).