msgb: Add may_alias attribute to struct libgb_msgb_cb

This explicitely allows aliasing of this struct to avoid the warning
shown below. Note, that this warning isn't show when
'-fno-strict-aliasing' is used.

Addresses:
gb/gprs_ns_test.c:85:54: warning: dereferencing type-punned pointer will
break strict-aliasing rules [-Wstrict-aliasing]
1 file changed