l1if: Add missing function prototypes

A few prototypes are not part of any header files, leading to
corresponding compiler warnings.

This commit adds the missing prototypes to sysmo_l1_if.h.

Addresses:
  sysmo_l1_if.c:347:2: warning: implicit declaration of function
      ‘l1if_transport_open’
  sysmo_l1_if.c:364:3: warning: implicit declaration of function
      ‘l1if_transport_close’
  sysmo_l1_fwd.c:89:3: warning: implicit declaration of function
      ‘l1if_handle_sysprim’
  sysmo_l1_fwd.c:91:3: warning: implicit declaration of function
      ‘l1if_handle_l1prim’
  sysmo_l1_hw.c:109:3: warning: implicit declaration of function
      ‘l1if_handle_sysprim’
  sysmo_l1_hw.c:118:3: warning: implicit declaration of function
      ‘l1if_handle_l1prim’

Sponsored-by: On-Waves ehf
1 file changed