Fix additional alignment issues for ARM platform.

Fix additional alignment issues for ARM platform.

This solves the following GCC warnings:

interfaces.c: In function ‘iface_minimal_checks’:
interfaces.c:421: warning: cast increases required alignment of target type [-Wcast-align]
interfaces.c: In function ‘lldpd_ifh_eth’:
interfaces.c:732: warning: cast increases required alignment of target type [-Wcast-align]
interfaces.c: In function ‘lldpd_ifh_mgmt’:
interfaces.c:1127: warning: cast increases required alignment of target type [-Wcast-align]