ar71xx: Fix FS#1805 (build failure for tiny targets due to -Wpacked-not-aligned introduced by GCC 8)

[hardfalcon]

Fix build failure for ar71xx tiny targets by correcting alignment for struct ipv6_destopt_hao in include/uapi/linux/ipv6.h

[xback]

I've compile-tested following targets as suggested in the FS ticket [1]

• tl-wa860re-v1
• tl-wr710n-v2

Both build fine.

Which compiler version are you using?

[1] https://bugs.openwrt.org/index.php?do=details&task_id=1805

[hardfalcon]

Like I wrote in the bug report, the build failure that this PR fixes occurs with gcc 8.2.

Using the default, which is gcc 7.3, the error doesn't occur.

For the sake of completeness: The error described in the bug report is probably triggered by -Wpacked-not-aligned which was introduced with GCC 8 and is part of -Wall.

[adde88]

This PR also fixes the exact same issue when tryingto compile latest master with the target being a WiFi Pineapple TETRA (custom code, trying to merge with master branch).

I got the exact same error message, and this fixes it.

[jow-]

Pulled into my staging tree at https://git.openwrt.org/openwrt/staging/jow.git