how to disable dma coalescing and check on or off in igc driver

[peterchan9]

https://www.intel.com/content/www/us/en/support/articles/000007456/ethernet-products.html

https://github.com/freebsd/freebsd-src/blob/releng/14.1/sys/dev/igc/if_igc.c    (freebsd 14.1)

https://github.com/freebsd/freebsd-src/commit/4c1441bba1d1bcc5a8237c97f136bf7e3cc77058#diff-b3c4dec5c5f214ce7f66e8fe5c7667c2a935a966d7b75da4719db52f0fc64defR498    (freebsd 14.2)