[GCC4] fix warnings in sdla_x25.c and sdla_x25.h

[GCC4] fix warnings in sdla_x25.c and sdla_x25.h

Removes most of these warnings with gcc 4 :

In file included from sdla_x25.c:107:
/usr/src/git/linux-2.4/include/linux/sdla_x25.h:59: warning: 'packed' attribute ignored for field of type 'unsigned char'
/usr/src/git/linux-2.4/include/linux/sdla_x25.h:61: warning: 'packed' attribute ignored for field of type 'unsigned char'
(...)
/usr/src/git/linux-2.4/include/linux/sdla_chdlc.h:65: warning: 'packed' attribute ignored for field of type 'unsigned char'
/usr/src/git/linux-2.4/include/linux/sdla_chdlc.h:67: warning: 'packed' attribute ignored for field of type 'unsigned char'
(...)
sdla_x25.c:321: warning: 'packed' attribute ignored for field of type 'char[15u]'
sdla_x25.c:322: warning: 'packed' attribute ignored for field of type 'char[15u]'
(...)