wpi: refresh manpage

[avos]

Summary

Reflect all recent changes in the manpage:

• add adhoc-demo and hostap into list of supported modes; add few examples for them;
• mention encryption/decryption offload for CCMP cipher;
• extend list of driver messages in the DIAGNOSTICS;
• document hostap mode limitations / powersave instability in the CAVEATS section.

Test Plan

$ igor man4/wpi.4
wpi.4:171:contraction:.It "wpi%d: [can't] map mem space"
wpi.4:174:contraction:.It "wpi%d: [can't] map interrupt"
wpi.4:177:contraction:.It "wpi%d: [can't] establish interrupt, error %d"