wil6210: accessing 802.3 addresses via utility functions

Rearrange the code by having functions to access 802.3 header
members, source and destination addresses.

Signed-off-by: Ahmad Masri <amasri@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Git-commit: 6d1ba32c8070bf9e4088b16d3af1eb2b6f05543c
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


[merez@codeaurora.org: SPDX license conflict]
Change-Id: Ib5417ce5ba77e5f96cb3b4d5d9cd322e78f39806
Signed-off-by: Maya Erez <merez@codeaurora.org>