Several cleanups and fixes to mxge:

• Remove vestigial null pointer tests after malloc(..., M_WAITOK).

• Remove vestigal qualhack union

• Use strlcpy() instead of the error-prone strncpy() when parsing EEPROM and copying strings

• Check the MAC address in the EEPROM strings more strictly.

• Expand the macro MXGE_NEXT_STRING() at its only user. Due to a typo, the macro was very confusing.

• Remove unnecessary buffer limit check. The buffer is double-NUL terminated per construction.

PR: kern/176369
Submitted by: Christoph Mallon <christoph.mallon gmx.de>